Undo manager for NSDocument

— still not working as intended
MBUserPreferences as a central point of preferences logic

-- plus upgrade to Xcode 6
Deployment target set to 10.10
beginSheetModalForWindow now use blocks
Project reverted back to 10.9
Improved handling of non-existing Java installation

— this is now default behavior on new Macs
— error dialog must be displayed on main thread
Fixed incorrect activity in XPC for fetching Java home
Fixed deprecated style for navigation bar
Code signing turned off

-- there is no reason to do so now and it only complicates build on OS X Server
Merge branch 'master' of https://github.com/algi/icecube

Conflicts:
	IceCube/Controllers/MBTaskRunnerDocument.m
	IceCube/Preferences/MBPreferencesWindowController.h
	IceCube/Preferences/MBPreferencesWindowController.m
	README.md