Centralized keyboard and drag events for BranchGraph

Converted BranchGraph to some sort of Class

Closes #2213

Redesign for navigation bar.

Allow proper use of @username in Git(lab|hub) Flavored Markdown.

Allow using a custom Gravatar URL.

Default is still set to the Gravatar.com service, but allows override
for a custom gravatar-ish service.

Renamed from gitlab:app:info
Add several extra info points

always use proper size value
do not show alt text when avatar image not loaded

fix failing spec

Spelling fix to rake info task

add rake task to gather system information

Fixes #1860

Closes #2196

Update pygments.rb

Fixes #1774

Fix for #1612 `overflow: auto` so content won't break layout

Devise locale updated to stay consistent with GitLab

add help page for gitlab specific rake tasks