verify if removal of syncable flag should be reverted or if bitmask client should be updated

The syncable property of Soledad was removed, but the bitmask client code was not updated accordingly.

We have to check:

• what is the meaning of that flag, and if its removal should be reverted.
• if it doesn't need to be reverted, how to fix bitmask client.

(from redmine: created on 2017-01-02)