Smart SQL for iOS

Just like Android, smartstore now really only knows how to run smart queries, other query types (exact, like, range) are converted to smart sql.

New class:
- SFSmartSqlHelper: takes care of converting smart sql to sql

New tests:
- SFSmartSqlTests: same native tests than Android

Some classes were renamed (to be consistent with Android and to reflect the fact that queries don't just target one soup):
- SFSoupQuerySpec -> SFQuerySpec
- SFSoupCursor -> SFStoreCursor

Note: external/shared still point to the unstable branch (because unstable20 has changes for bootstrap which are not yet supported by iOS) and therefore javascript smart sql tests are failing and doing a smart query from javascript is not supported.