Make text about password not matching appear only when passwords don't match.
Change width of dialog window, to make it look better.
fixes points 1 and 2 from issue #2337
@apprb there is one question and one TODO that you should look over in privacyform.cpp, as well as a TODO in historykeeper.cpp
Also both the encryption settings box and the pw dialog lineedits should probably be in a QGridLayout... but I don't really want to do that by hand :P
Things are left to do:
1. load/save encrypted tox datafile
2. incorrect passwords processing (ask to retype, wipe everything, etc.)
3. reencryp history log with new password
