Add 'New Profile' sheet (wip).
Hoist profilesList into the Singleton class.
Change Singleton implementation.

Switch from CocoaWithLove/CWLSynthesizeSingleton.h
to http://www.galloway.me.uk/tutorials/singleton-classes/.
Absorb NewProfileController into LeftPaneController.

The reason for this (not so good, as LeftPaneController is
becoming too fat) change is that I need to access profilesTable
and profilesList when closing the sheet, and I didn't figure out
a good way of passing data (maybe use contextInfo of
didEndSheet to pass in the whole LeftPaneController?).
Switch on ARC (remove AppDelegate's dealloc).