Added offline support ( using sqlite database & cordova file plugin )

• Now the list of documents on the media page is in synchronisation with the resources uploaded on the dhis2.

• List of documents on the media page will be available in offline mode also.

• For every document when the user clicks, if it is already downloaded it will be played using the fileopener2 Cordova plugin

• If the user is connected to the internet then whenever he clicks on the document it will get synced with the dhis2 and a new copy will be saved to File System local device, Corresponding file location will be updated to SQLite-DB as well.

• A separate icon is also placed on every document to show its sync status

• On ongoing sync, a progress bar is visible on the document.

Related Issues: #69 (closed)