Facility to (re)store font size preferences

[TimBaldwin]

When demoing in the lecture theatre (and tutes), it would be good to be
able to selection a particular font size setting more efficiently than
Ctl-Shift-= a bunch of times in the right windows (e.g. I generally want
the editor and console, but not the frame to be of larger size, which is
always fiddly). It would also be good to have a keybinding to 'hide' the
console, as when the font is too big (again in a lecturing setting), the
'hide' icon disappears from the browser window. I guess ideally, I want to
be able to save a couple of 'profiles' for font/window size preferences,
for demo and personal use, and to be able to select between them quickly.