LatinIME: Add fallback loader for JNI lib

Prefer the JNI lib with gesture typing support.
If not available / installed fall back to the standard one without
geture typing.

Change-Id: I70a5f43386a9c72809a70bd286f3702378d6f9be

LatinIME: Only enable gesture mode if gesture lib is available

 * Prevents keyboard FC when gapps is not loaded.

Change-Id: I0d48e1cd80534513205f61913c798b48573ea38c

LatinIME: Remove gesture preference if gesture lib is unavailable

Gesture typing won't work without the gesture library,
so remove the preference to not mislead users
into thinking that gesture typing is supported.

Change-Id: I387ae83fd174b57fc48fe7bcfc37e3010ce89b12