Improve Bluetooth tethering UI usability.

- Updated hint text for BT tethering checkbox to
  "[Sharing|not sharing] this [tablet|phone]'s mobile data connection".
- Show correct hint text when user enters tethering screen.
- Show correct status after user enables tethering when Bluetooth is off.
  When BluetoothPan.setBluetoothTethering(true) is called with BT off,
  BluetoothPanProfileHandler will add a broadcast receiver to enable
  tethering after BT turns on. This happens too late to show the correct
  status when TetherSettings gets the adapter state changed event, so set
  a flag (mBluetoothEnableForTether) instead, and call setBluetoothTethering
  ourselves after the state changes to ON. Also, clear the flag if the
  adapter state changes to OFF or ERROR.
- Show correct status when user enables tethering, then disables Bluetooth,
  then returns to the tethering screen. Previously it would show
  Bluetooth tethering enabled, even though adapter state was OFF.
- Show the number of connected devices in tethering preference screen.
- Distinguish between PANU and NAP in device profiles screen, and show
  appropriate text to clarify the direction of tethering.
- Remove profiles from device profiles list when the device removes the UUID
  (e.g. Mac OS X turning NAP on/off) and after a NAP disconnection when the
  remote device only supports PANU.

Bug: 3414575
Change-Id: I2c0830876d5b9bddb293e57c4d3ca74f105911b8

src/com/android/settings/bluetooth/LocalBluetoothProfile.java

@@ -60,8 +60,9 @@ interface LocalBluetoothProfile {
     /**
      * Returns the string resource ID for the disconnect confirmation text
      * for this profile.
+     * @param device
      */
-    int getDisconnectResource();
+    int getDisconnectResource(BluetoothDevice device);
 
     /**
      * Returns the string resource ID for the summary text for this profile