better layout and animate keyboard

Summary:
Similar to D4893, use a state machine to track the status of the
keyboard and animate the open/close.
this improves also the layout on low and weird resolutions when
there isn't much available space

Test Plan:
tested with many different window sizes, to make sure it
behaves better than before

Reviewers: Plasma, davidedmundson, graesslin, broulik

Reviewed By: Plasma, broulik

Subscribers: apol, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D5254