Reworked the PasswordGeneratorWidget.

It's loosely based on OS X PasswordAssistant. Generation happens as soon as a
change is made, and on open of the widget. A combobox has been added to allow
one to choose from some randomally-generated alternatives, and the UI is
generally been made a bit more compact.

Written by Michael Curtis <michael@moltenmercury.org> and revised by me.

Closes #119

https://github.com/keepassx/keepassx/pull/38
Move password generator widget to the right row.
Uncheck the correct widget in ChangeMasterKeyWidget.

We want to enable the password group but mask the password in the line edit.
Merge remote-tracking branch: upstream/master