Add start call to QML

Add start call to QML

Tweak the app QML to call into the new start call in the libqtappfw
Mediaplayer object that replaces the previous WebSocket onConnected
hook.  This is driven by the need to hold off triggering events from
the underlying libqtappfw Bluetooth object until the QML engine is
running, otherwise it misses events driven by bluez-glib
initialization querying BlueZ state.

Bug-AGL: SPEC-4231

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: Ia4c98a19c73aaf778d4133ef77d93bfdacdf7974