changed image keys from strings to Guids; added more context for Remotes and remote-tracking branches;
Changed image keys from strings to Guids, for preventative reasons.
Added context information when a Remote is setup as a push mirror.
Also added context for a Remote's URLs including whether or not they differ.
load/save RepoObjectsTree splitter position in Settings;
RepoObjectsTree splitter position is now loaded and saved from Settings.
RepoObjectsTree splitter was auto-sizing and causing issues;
To repro:
  1. set MainSplitter Bindings to size in Settings
  2. select a commit in RevisionGrid
  3. resize RepoObjectsTree splitter
  4. select [Diff] tab and resize its splitter
  5. select [Files] tab