Added variable speed playback control as a global option.
Merge pull request #186 from TheRealFalcon/playback-speed

Bug fix for trying to set speed/pitch when media is null.
Merge branch 'playback-speed' into speed

Conflicts:
	res/values/arrays.xml
	res/values/strings.xml
	src/de/danoeh/antennapod/activity/PreferenceActivity.java
	src/de/danoeh/antennapod/service/PlaybackService.java
Variable speed playback as user preferences and customization of playback speed.
Merge branch 'speed' into playback-speed
Reduce default speeds to every .1 instead of every .05 so user doesn't have to do a lot of unchecking.  Also, be consistant about where float or double is used and be consistent about which context is used for UserPreferences.