Added a daemon mode to aapt to receive streams of commands from gradle.

When crunching png, we used to spawn a separate aapt process from java
which is slow and resource intensive.
Introduced a daemon mode to appt which when invoked with -m parameter
will listen from commands on stdin and give report of command execution
on stdout.

One one command is supported so far :
s f1 f2

This command perform a single png crunch, f1 pointing to the input
png file to crunch, and f2 pointing to the path for the resulting
crunced file.

Expected output from the command is "Done" or "Error".

Change-Id: Iaf1d865e8d5ee5d36abe39dea6443715865a98d3