CharacterMap: select Unicode block for current character

* Scrolling the list of characters now selects the currently visible
block in the blocks list.

Signed-off-by: Adrien Destugues <pulkomandy@gmail.com>

Fixes #3651, part 1
Notifications default to enabled on first boot.

* The server did this right, but the preflet would not check the
checkbox when there was no settings file.