Add timestamp support into core mobile filter framework.

Add timestamp support into core mobile filter framework.

Timestamps are positive longs representing nanoseconds from some
starting point, the exact definition of which depends on the frame
source filter.

The base filter class will fill in a timestamp on all output frames
based on the first pulled input frame's timestamp, if the filter
process() method doesn't set the output frame's timestamp itself.

Programs should get timestamps passed to them using setHostValue().

Change-Id: I89f73903f7c36fd8e01d5d1a8c49c53063f216bb