Layout and animations on the on screen keyboard

Summary:
use a state machine to define in a cleaner way
the layout of the lock screen when the keyboard is
open on closed. animate between the state changes with
a slide animation
Depends on D4870

Test Plan:
tested opening the keyboard with different screen locker sizes
to see the text field and the button always stay visible

Reviewers: graesslin, Plasma, broulik

Reviewed By: Plasma, broulik

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D4893