Project activities perfomance increased. Cache for project activitites disabled. Repository conception changed

Implementation is correctly done through observer.

I have to domesticate RubyMine, keymapping is not the same as IntelliJ and I have deleted a character by mistake...

2/ @commit.safe_message as an argument
3/ preserve in helper
4/ spaces around operators

It matches #[0-9]+ in commit messages.
For example
 * Fix for #12
 * Code review for #56
 * Test for #15, Review on #54, Fix for #42

 It only links to valid issues (existing and belonging to the current project)
 It does not add any link to the commit in the issue page, it only consists in parsing the commit message when displayed.

 This can be considere as a primary work for the issue #155 on gitlabhq/gitlabhq.

Allows to alert only the commit author when a new note is added on a commit, useful when gitlabhq is used for code
reviews, allows less noise with mails...

Users with many projects (>100) will hit the 20 second timeout when
updating the gitolite config. This fix batches those changes into a
signle update to the file, causing an order of magnitude speed increase
which finishes well below the 20 second timeout.

Fixes gitlabhq/gitlabhq#220

This reverts commit f80745b7.