Password: Port to Adwaita style

A fairly small amount of work to port the password page to use AdwPasswordEntryRow. Note that I used a separate AdwPreferencesGroup for the password and the confirmation as each has its own message below for an explanation or error, and the LevelBar in the case of the password.

As long as I'm here, I've updated the LevelBar styles to use Adwaita named colors instead of hardcoded hex values.

master	this branch

I was unsure about exact spacing values, so feedback is more than welcome!