Moved Drive file id caching to chrome.storage.

Also removed file ids from the cache when files are removed.
Added remote-to-local deletion syncing.

Also added a couple of function comments.
Refactored Drive id caching functions.
Added caching for the next change id.

Change retrievals from Drive are no longer duplicated across multiple runs.
Added a button to clear Chrome storage.
<a href=> links pop out to system browser
Adding android alarms.
Cleaning up android alarms.