Add-KML plugin support for IITC Mobile

Currently Add-KML plugin does not work in IITC Mobile, as HTML file input is not supported by Android webview, but the plugin depends on HTML file input to pick a KML/geoJSON/GPX file to open.

To support add-KML in IITC Mobile I added a pickKmlFile method to IITC_JSInterface which starts a file chooser intent, reads the selected file and passes the content of the selected file back to the method addKml in the javascript of the add-kml plugin.