Improve support for touch in the folder window

Folder window is not optimized for touch.

While you can select the different folders if, select to collapse the folder list of the email account you cannot select to expand it again. And you have to close Geary and reopen it again to get the list of all the folders.

Or maybe I need smaller fingers?

I think it would make sense to also make everything larger in the folder window. There is plenty of space horizontally, not even halt of it is used as it is now.

mentioned in merge request !10 (merged)

closed via merge request !10 (merged)

mentioned in commit 7644e034

Yay!!!