…ncurrently

For concurrent ui flows, we register the connection of the current flow
which is immediately picked up by the viewmodel. Another ui flow might
run and register a connection to be picked up by its viewmodel, and by
the time the first ui flow is done and tries to remove the iconnection
registration, that iconnection is not the one it registered any more. So
we're not removing registrations any more, and we just let the
UIController replace the IConnection any time it needs to launch a new
viewmodel.

…t() method

We already support showing a separate dialog for authentication, but it
only worked when the selected ui flow was either authentication or the
clone/create flows, which reuse the same dialog window. It also worked
for publish, but that one is actually cheating by running two separate
ui flows (the auth and then the publish)

Since we now support long running ui flows that switch to subflows when
needed, we need to be able to show a view in either the pane or in the
dialog, basically popping up the dialog whenever needed and then
shutting it down without stopping the ui flow.

Fixes #282

We were getting into a state when loading the pane for the first time
where `Reload` would be called once as a result of the `RepoChanged`
call, which triggers when `Initialize(ServiceProvider)` runs, and then
`Reload` would run again as a result of the `Initialize(ViewWithData)`
call, because the Pull Requests button was clicked, which causes the
pane to reset itself. These two `Reload` calls would be executing
concurrently, causing a race condition that would crash randomly if the
controller was stopped and restarted at just the right point.

Need to make sure that nothing else can happen while
`Initialize(ServiceProvider)` is running, and that
`Initialize(ServiceProvider)` is run serially (no asyncs here!).

Polish Pull Request list view

[WIP] Add Pull Request Creation View

https://msdn.microsoft.com/en-us/library/mt162316.aspx

Replace hardcoded fontsizes with proportional text styles

Bump feature/pr/views version to latest alpha

Pull Request list view and viewmodel