add rake tasks for web hooks management
add help page for web hooks management using rake tasks
Update logic for validates_merge_request for tree of MR

For case:

Merge request №1: branch "feature" to "release" and remove "feature" branch

Merge request №2: branch "release" to "master" and remove "release" branch

Merge request №1 - broken :(
Fixes grack authentification under relative_url_root

Ref: https://github.com/gitlabhq/gitlabhq/commit/e6159b8725f99af78f446f8d33fa0e52b7780430
Ref: https://github.com/gitlabhq/gitlabhq/pull/3204
Ref: https://github.com/gitlabhq/gitlabhq/issues/1228

Add Rails' variable in application.rb to support relative url

This variable is used by assets compilation and other modules.

Note that user needs to change application.rb too

Restrict session cookie to the relative path if set.

Ref: https://github.com/gitlabhq/gitlabhq/commit/2c2f1e31856a4decdae469974f5bea8245316f7e

Fix Update attachment_uploader.rb bug with relative URL

See: https://github.com/gitlabhq/gitlabhq/commit/161afda3fa4fca58f396e9c3acbd72bc14490ace

Fix Wall relative bug with attachement files (javascript)
Remove -y option when removing puby1.8

Since it is easily could break installations running on the server - hence the person doing the install should be able to make the decision to remove himself.
Make flash messages fixed and sticked to bottom
Update flash message timeout to 5 seconds
Merge pull request #4797 from mbajur/flashes-revived

Make flash messages fixed and sticked to bottom
Merge pull request #4670 from anezi/relative-url-patch

More fixes for supporting Relative URL
its time for beta
Make repo graph work for large repos on slower machines
Add iid field to issues and MR
Sett iid on create. Use iid as value to_param
Create task to create iid for existing issues/mr
Find issues and Mr by iid in controller
Show iid as default id for issues, mr
Show iid in event feed and uatocomplete as default id for issues, mr
Configure the relative path only one time.
Iid improvemets

* call set_iid before validation
* make rake task pass event if objects are invalid
* show iid in comment event at dashboard
Fix confusing situation where install guide told you to install init.d script for puma.