Second optional parameter for Utility.GetIcon - pointing out the 2x icon

Feature/history broad mode

Feature/branches

# Conflicts:
#	src/GitHub.Unity/Assets/Plugins/GitHub/Editor/Settings.cs

Double-click remote branch to create a new local branch tracking it. Only allow this as well as switching when in default mode.

Properly read file names with '@' in them when doing git status.

Show tracking icon next to local branches tracking as well as next to remote branch being tracked by selection.

Feature/history arrow navigation

Simple settings override