Add on/off switch for automatic DC cancelling.
Move input device settings I/O to DockInputCtl.
Store receiver settings (issue #58).

Following settings are saved:
- Demodulator (mode)
- Filter offset
- Squelch level
Update news.txt
Use 1 second time constant for DC correcftion.
No need to calculate sample period for DC correction.
Update news.txt for new snapshot release.
Updated.
Fix spelling error.
Fixed current device selection in config dialog.
Merge pull request #60 from nhasan/master

Fix current device population in config dialog
Updated.
Fixed audio output device (PA) selection.
Fix the "back to default" case.
Merge pull request #62 from nhasan/master

Allow using audio output device other than the default one.
Updated.
Save and restore audio gain settings.
Merge pull request #63 from nhasan/master

Save and restore audio gain setting.
Add support for automatic I/Q balancing.
Add info about gr-iqbal component.