Fix LT-15205 where SFM imports were duplicating entries

Change-Id: I91431422eb82c779ed544f2f134690ee91e92646
LT-15204: Keyboards Forgotten

Merge keyboards from the Local Store into user.config
Note: this now saves default keyboards in user.config
Add unit test; fix existing unit tests.
Clean up PalasoWritingSystem a bit.

Change-Id: If55325247bcf74f364bd870295945242e97a9e6e
Signed-off-by: Hasso Pape <hasso_pape@sil.org>