Compile gsfProxy into our builds

[petefoth]

This is the ticket: microg/GsfProxy#17
The fix is already merged in the GsfProxy repo but no new version was released.
The problem is just that apps may not see GsfProxy and so making GsfProxy usless but it doesn't cause real issues (beside C2DM not working).

An idea: since GsfProxy is small and doesn't have issues with signature maybe you can also compile it together with the ROM.

Originally posted by @ale5000-git in #78

[petefoth]

But see this comment re: possible signing issue of we do this

But if we do that, I think we will run into signing issues: the
GsfProxy in our current builds is signed by microG , but if we make
our own build it will be signed with our key. I expect that will
lead to problems when 'dirty flashing'. And the 'benefit' of
including this change is probably not enough to be worth the hassle
of handling the signature difference.

Or have I missed something?

[ale5000-git]

You could try to replace an apk manually in the system partition with another one with a different signature in a phone, at most it lose app data and the installed updates of the changed app in the data partition.

So it may lose the app data of GsfProxy, but this app doesn't need any data so it is fine.