[2/3]OmniGears: 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.

Base: https://gerrit.omnirom.org/#/c/4370/
Settings: https://gerrit.omnirom.org/#/c/4372/

Change-Id: If4e2ae97175c9f81ecfc1c9896ed1ab27448d558