Add .mpga to acceptable file name extensions list.

The *.mpga files are playable, but are not correctly scanned.
This is because they are prevented from being scanned in
StagefrightMediaScanner.cpp.
What this fix does is to add the extension to the list of valid
file extensions so that the scanner handles the filetype properly.
We have previously added the .mpga extension to the framework to
make it playable, but not added it so that the scanner scans it.

Change-Id: I02a44d770adb80d38e8bed77d0d76efa1b28a861
Changed parsing of trkn and disk from 8 bits to 16 bits

The MPEG4Extractor was parsing 8 bits instead of 16 bits when parsing
'trkn' and 'disk'. Also added support for 16 bytes size 'disk'.

Change-Id: I22b4de2ac800881884d5759776cb380917522a87
Merge "Add .mpga to acceptable file name extensions list." into jb42
Merge "Changed parsing of trkn and disk from 8 bits to 16 bits" into jb42