SoundRecorder: Fix back key no response in pause state

In the function onKeyDown(),there is no operation to
handle back key event of pause state

Add a case to handle the pause state when click back
key.

CRs-fixed: 643473

Change-Id: Ifc031917735ce6ea8283977428547835ab2bf31e
audio: Reset mAudioSourceType once call disconnects

-After ending the call while in recording, handset mic gets
selected for subsequent recording sessions though headset is
inserted, unless application is exited.
-mAudioSourceType remains to be VOICE_UPLINK in sound recorder
app when voice call is disconnected.
-Reset mAudioSourceType once call disconnects.

Change-Id: Ida4bebad3960bead7a1376c381927671553e3dfc
CRs-Fixed: 636368