Changes done to list recordings

Removed Custom adapter and now using Expandable list view to display
recordings
small simplification of loadRecordingList.
moved date formatting out of data model class into activity class.
renamed layouts to reflect their type:
activity_* layouts represent complete activities only
changed list header style to orange
layout tweaks for ListRecordings
added explicit method getNameFull() to Task class to get the task path including all parent tasks.
This is an alternative way to the toString() method producing the same result but making the usage more obvious.