[1/3]Base: Add keyboard features

this commit adds:

- ime switcher notification - thanks cm
- slims fullscreen disable on landscape
- slims force autorotation on IME
- volume button control for navigate in the message - thanks cm
- slims force to show always enter key

some fixes to the 4.2/4.3 implementations + added full multiuser
support for all these features.

OmniGears: https://gerrit.omnirom.org/#/c/4381/
Settings: https://gerrit.omnirom.org/#/c/4372/

Change-Id: Ie2672e69816afa2571bf6611caa95754ea29cd93