Using the API library to create or update a merge request at the moment a 404 error is returned.
This is fine when the merge request in question does not exist, but does not provide good
information that for example a required attribute is missing.
A status code of 400 (Bad request) is returned when creating or updating a merge request
when either `source_branch` or `target_branch` is missing. A status code of 409 is returned
when `source_branch` and `target_branch` are the same. Tests are added for these cases.

correctly describes the new behavior

The attempt to revoke project access for a user that was not member of the
project results in a 500 Internal Server error where it actually should
result in a 200 OK since after the operation, the user is not member of
the project. This turns the operation into an idempotent call that can
be repeated with no ill effects.

Updated the spec and changed the code accordingly. However, the result differs
slightly, as we can't return the users project access level if the user was not
member. I'm not aware if anybody relies on the result of this call.

Fixes #2832

In case we rescue from a fatal error, we want the error and the backtrace to
the error logged, so we can debug later on. This change injects the configured
logger from the rails app to the grape API and logs error as well as backtrace
in a rails-like fashion.

This rescues all errors and returns a proper JSON response. Fixes #2833.

Fix #2790

remove incorrect information about the api version

The API version is currently not equal to the gitlab major version number. Gitlab 4.1 
still uses API version 3. Point to the lib/api.rb file instead which contains the
autoritative information.

Added swipe view for image diff

Prepared diff view for multiple view modes

Converted commits.js to coffeescript
image info in separate coffeescript file

Added swipe view mode

Added onion skin viewMode

Updates web hooks to process via queue

Feature: Projects page

Missing environment added to 'Try fixing it' block

fix edit project members access link and page fixes refs #2745