MOTECH-1213: Commcare get calls for cases/forms limited to 20

This commit adds paging Api to commcare module, also removes unused API getAll.
This change also fixes:
- JSON Button for forms and cases
- Bugs in forms displaying
- NumberFormatException when GSON is deserializing data from commcare domain

Change-Id: I1640f82e04bb3918ca49f8a0499c2b96b7b20d5d