camcorder pause feature

--libmedia: add pause() interface in MediaRecorder and IMediaRecorder and add Pause state in mediarecorder's state machine
--libmediaplayerservice: add pause() interface in MediaRecorderClient and StagefrightRecorder
--libstagefright:      1.stop-in-pause implementation in recording pipeline for pause feature;
--camerasource: support switch between start() and stop()
--audiosource:  support switch between start() and stop()
--soft aacenc component:  clear some variables when doing flush to support re-start
--soft amrnbenc component: clear some variables when doing flush to support re-start

Change-Id: I3036ef8f4cc7644c1d36aa0b19e64fc9dc12c1f8