Add "Dump HPROF file" to DDMS/DDMS plugin

Add "Dump HPROF file" to DDMS/DDMS plugin

This uses the (new in cupcake) VM command through JDWP.
Older VMs are detected through the (also new) 'FEAT' command that notifies
which features the VM supports.

The hprof file is right now saved in /sdcard. Due to donut+ apps not having
the SD Card permission by default, we may need to change this in the (near)
future.

Upon completion of the dump by the VM, DDMS will give the user a file selector
to choose a place to save the file on the host machine.

Future improvements: run (our own) hat, or hprof-conv and a standard hprof
tool (Eclipse MAT integration for instance). This should be configurable
by the user.

Change-Id: I33696b0263e3d0788ad5d90cedf3cd17393d2f9b