Move config_accessor :asset_host from ActionController::Base to AbstractController which fixes issues with asset_host in ActionMailer

Including:
  - Moved mailer objects in separate directory
  - Added two tests for asset_host configuration option

Signed-off-by: NXavier Noria <fxn@hashref.com>

Commit f7ba614c improved the internal consistency of the different
means of accessing routes, but it introduced some problems at the level
of code comments and user-visible strings.

This commit applies fixes on three levels:

Firstly, we remove or replace grammatically invalid constructs such as
"a routes" or "a particular routes".

Secondly, we make sure that we always use "the router DSL" or "the
router syntax", because this has always been the official terminology.

Finally, we make sure that we only use "routes" when referring to the
application-specific set of routes that are defined in the
"config/routes.rb" file, we use "router" when referring on a more
abstract level to "the code in Rails used to handle routing", and we use
"routing" when we need an adjective to apply to nouns such as
"url_helpers. Again this is consistent with historical practice and
other places in the documentation.

Note that this is not a sweep over the entire codebase to ensure
consistent usage of language; it is just a revision of the changes
introduced in commit f7ba614c.
Signed-off-by: NWincent Colaiuta <win@wincent.com>
Signed-off-by: NJosé Valim <jose.valim@gmail.com>

[#4979 state:committed]
Signed-off-by: NJosé Valim <jose.valim@gmail.com>

Signed-off-by: NJosé Valim <jose.valim@gmail.com>

The documentation makes it sound like mail() only accepts a limited
set of headers in the headers hash, but it in fact accepts any
arbitrary headers, and there is a test ("can pass random headers in
as a hash to mail") for it in the test suite.
Signed-off-by: NWincent Colaiuta <win@wincent.com>

Move Rails::LogSubscriber to ActiveSupport::LogSubscriber, allowing frameworks like ActiveRecord and ActiveResource to log outsude Rails::Application [#4816 state:resolved]

Signed-off-by: NJosé Valim <jose.valim@gmail.com>

Signed-off-by: NJosé Valim <jose.valim@gmail.com>

[#4843 state:resolved]
Signed-off-by: NJosé Valim <jose.valim@gmail.com>

subject is automatically looked up on I18n using mailer_name and action_name as scope as in t('.subject')

Signed-off-by: NJosé Valim <jose.valim@gmail.com>

Signed-off-by: NJosé Valim <jose.valim@gmail.com>

Signed-off-by: NJosé Valim <jose.valim@gmail.com>

[#4645 state:resolved]
Signed-off-by: NJosé Valim <jose.valim@gmail.com>

[#4626 state:resolved]
Signed-off-by: NJosé Valim <jose.valim@gmail.com>

[#4610 state:committed]
Signed-off-by: NJosé Valim <jose.valim@gmail.com>

Changed encoding behaviour of mail, so updated tests in actionmailer and bumped mail version to 2.2.1
Signed-off-by: NJosé Valim <jose.valim@gmail.com>