[3/3]Settings: 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/
OmniGears: https://gerrit.omnirom.org/#/c/4381/

Change-Id: I0420047cf24b5f0baa3b9eebfae5ab6800f14c7a