fix an issue w/ sizing of the ace editor; delay hiding the splash screen

Fix an issue w/ the ace editor not being sized properly when tabs changed between showing and not showing states. We need to re-size the editor when it's vertical height changes.

Also, move to hiding the splash screen when more of the app is ready. We now wait until after the workspace is restored. Before we waited until after polymer was ready. This prevented FOUC but left the components empty until the app was loaded.

@dinhviethoa @ussuri