[2/2] LatinIME: get rid of the prebuilt dictionaries

reduces apk size by about 30mb.
allows to download the dictionaries per request.

not every user needs dictionaries, and the ones who need it do not need
EVERY single dictionary.

remove the prebuilt dictionaries, only keep empty and main, allow to download
the dictionaries if not existing or install it from sdcard.
(Nameless/LatinIME)

Vendor side: http://gerrit.nameless-rom.org/#/c/840/

Change-Id: I1dff1b171dd9e7a36164bc3ea869e95b0f3d1048