Add branch visibility, consolidate branch actions

[weihwang]

UX goals: Increase visibility to target branches, in preparation for push/pull actions. This proposal also addresses issue #224 by focusing on git repo information in the header. Consolidating actions to the local/remote branches into an update modal gives us a clear header, and one place to take action on branches. https://www.figma.com/file/UyNpeQNuTj6Uv74MoEJDh3ji/Git-extension?node-id=524%3A3110. Pre-requisite UX change for #234

Existing UI

v1 + visibility to remote branch

v2 + ability to update local/remote branches

[tgeorgeux]

Looks Great 👍

[telamonian]

What was this issue supposed to be about, and should we still be concerned about it? The mockups are hard to parse, and aside from the text alignment I can't tell the difference between the first two.

@tgeorgeux Can you please interpret?

[fcollonval]

@telamonian @kgryte I think this can be closed.

[kgryte]

Agreed.