Merge remote-tracking branch 'drebs/feature/2277-add-sqlcipher-api-to-sqlcipher-backend-2' into develop
Merge remote-tracking branch 'drebs/feature/2359-avoid-encoding-problems-when-storing-u1db-data' into develop
Move symmetric encryption/decryption code from leap.common to leap.soledad.
Encapsulate leap_assert so we can not depend on it.
Remove dependency on leap.common.files.mkdir_p().
Encapsulate signaling so Soledad does not strictly depend on leap.common.events.