Usability: obvious simplifications

1. Very simplified color picking:
Press i (or your customized shortcut). Once you pick a color, the tool
changes back for you, to its previous state.
( Alt key is no more used for being a bit obstructive, especially when
navigating through windows,  you will like this new way, for sure)

2. More comfortable and simpler dynamic cursor, just Shift key now:
X move: changes width
Y move: changes feather

3. Minimum size set to most practical values: width 1,  feather 1