This ensures Rails and Sidekiq transactions are split into the series
"rails_transactions" and "sidekiq_transactions" respectively.

This removes the need for any tags to differentiate between Sidekiq and
Rails statistics while still being able to separate the two.

This makes it easier to see where time is spent without having to
aggregate all the individual points in the method_calls series.

This will be used to store/increment the total query/view rendering
timings on a per transaction basis. This in turn can greatly reduce the
amount of metrics stored.

Attempting to use the /projects/:id API by specifying :id in
"namespace/project" format would always result in a 404 if the namespace
contained a dot.

The reason? From http://guides.rubyonrails.org/routing.html#specifying-constraints:

"By default the :id parameter doesn't accept dots - this is because the dot is
used as a separator for formatted routes. If you need to use a dot within an
:id add a constraint which overrides this - for example id: /[^\/]+/ allows
anything except a slash."

Closes https://github.com/gitlabhq/gitlabhq/issues/9573

This isn't hugely useful and mostly wastes InfluxDB space. We can re-add
this whenever needed (but only once we really need it).

This removes the need for tagging all metrics with a "process_type" tag.

This ensures we don't need to load anything from either PostgreSQL or
the Rails cache whenever creating new InfluxDB connections.

This particular setup had 3 problems:

1. Storing SQL queries as tags is very inefficient as InfluxDB ends up
   indexing every query (and they can get pretty large). Storing these
   as values instead means we can't always display the SQL as easily.
2. We already instrument ActiveRecord query methods, thus we already
   have timing information about database queries.
3. SQL obfuscation is difficult to get right and I'd rather not expose
   sensitive data by accident.

Nokogiri produces inefficient XPath expressions when given CSS
expressions such as "a.gfm". Luckily these expressions can be optimized
quite easily while still achieving the same results.

In the two cases where this optimization is applied the run time has
been reduced from around 170 ms to around 15 ms.

Around 300 ms (in total) would be spent in these delegated methods due
to the extra stuff ActiveSupport adds to the compiled methods. Because
these delegations are so simple we can just manually define the methods,
saving around 275 milliseconds.

This is a tad faster than letting Nokogiri figure out whether it should
evaluate the query as CSS or XPath and then actually evaluating it.

While it's useful to keep track of the different versions (Ruby, GitLab,
etc) doing so for every point wastes disk space and possibly also RAM
(which InfluxDB is all to eager to gobble up). If we want to see the
performance differences between different GitLab versions simply looking
at the performance since the last release date should suffice.

This ensures we can still start up even when not connecting to a
database.

This removes the need for Sidekiq and any overhead/problems introduced
by TCP. There are a few things to take into account:

1. When writing data to InfluxDB you may still get an error if the
   server becomes unavailable during the write. Because of this we're
   catching all exceptions and just ignore them (for now).
2. Writing via UDP apparently requires the timestamp to be in
   nanoseconds. Without this data either isn't written properly.
3. Due to the restrictions on UDP buffer sizes we're writing metrics one
   by one, instead of writing all of them at once.

Newlines aren't really needed and they may mess with InfluxDB's line
protocol.

This ensures we can still boot, even when the "application_settings"
table doesn't exist.

Needed to support Huboard

`runners_registration_token` now creates a new token if it is blank.

This standardizes all the project API formats. Also needed to support Huboard.