Change storage from local to sync

[allen505]

Change the default storage location from local to sync. Some key points to consider:

• Setting up IDs for in browser_specific_settings, especially for Chrome and other Chromium based browsers
• Sync size(100KB) is lesser that local(5MB). Exception handler for out of storage must be in place, warning the user. A fallback to local should be done.
• Research needs to be done to see how many tabs need to be saved before the storage fails, and if it is feasible.
• If the browser is not signed in or user wishes to opt out of sync, it should fall back to local
• Syncing when there is no connection
• Duplication of saves on local storage and sync storage must be avoided

Helpful links: storage.local storage.sync