Review 'users' and 'groups' administration sections on consistency and polishing

The users and groups sections in administration is currently in a really bad shape. There are:

• translation inconsistencies in terms of wording (add vs create and alternating between them in the same screen)
• translation key usage free-for-all; using "rightsmanager", "xe.admin.groups", "platform.core.rightsManagement", "admin.groups", or worse, not translated strings.
• manually created livetables instead of using the livetable macro
• inline javascript (a lot of it), both in the DOM and in on* attributes
• etc.

IMO, it`s a critical section that we should have in top shape.