Updated canvas test case to comply with the new and narrower mpp range
gui settings: force subset of values for DELPHI accel voltage and spot size

as requested by users, because it's not convenient to be able to select any value of
voltage and spot size. It's much faster and precise to pick among a few useful set.
phenom driver: change display of spot size unit

use unicode powa
Merge branch 'master' of vpn.delmic.com:odemis
gui controller: move back the toolbar code to the tab controller

was supposed to be handled by the view controller, but could only add one button.
Simpler to just do everything in the tab controller.
gui stream controller: force the current view to contain the stream when playing it

When starting a stream, if it's not currently visible, it's weird to be sent to another view,
which has the stream visible.

It's much simpler for the  mind if the stream automatically becomes visible in such a case.

Of course, the view has to be compatible. So that if starting the SEM while watching an optical
view, the user is still sent to the SEM view.
refactoring: use MetaClass instead of list for defining generic type of streams

It's more pythonic to use metaclass. Shouldn't have any behavioural change.