Git: Add on-demand branches expanding

Make "branches expanding" on demand and asynchronous.
After "git show" there is clickable text: "Branches: <Expand>" in
description. If user clicks this text then branches for commit is
triggered and done asynchronously.

Task-number: QTCREATORBUG-11293
Done-with: Przemyslaw Gorszkowski <pgorszkowski@gmail.com>
Change-Id: I772cfef823d3f95e2b3060dfb5973157d81fc11a
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Git: Remove diff editor

Not used anymore

Change-Id: Ie1c79583938e24c3bad8acad7acc2f0574234450
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
QbsProjectManager: Added functionality to remove files from projects

Change-Id: I3371e14b5fbf2eaaacc833b289f945aed57cc80e
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Help: Open example documentation in extra window

Also remove the hack that HelpManager::handleHelpRequest looks
for ?view=split in the URL and use an enum instead.

Change-Id: I4ad74775381cf0b321181358266d8e89c6e277b5
Reviewed-by: Karsten Heimrich <karsten.heimrich@digia.com>