Spectrum Spectrogram Analyzer

Feb 28, 2017

Major changes:
* Add log frequency axis plot to both spectrum and spectrogram.
* For new devices (>=Android 6.0), now a dialog is added to require permission to read from microphone and write to file.
* Add dialog to set frequency view range exactly and possible to lock the range.
* Fix various crash (e.g. choose a non-usable audio source).

Improvement:
* Keep view range when change sampling rate.
* spectrogram shift mode slightly more smooth.