Names for sync

[wmathurin]

• New methods in plugin: getSyncByName, deleteSyncById, deleteSyncByName
• (Optional) syncName argument in syncDown and syncUp
• Mock implementation (to be able to test in a browser)
• New tests
• Some misc refactoring of the code that keeps the plugin backwards compatible

[wmathurin]

Pointed my android repo to that code and was able to run all hybrid tests and the smartsyncexplorer hybrid app successfully.