Fix python2 for webview

[KeyWeeUsr]

new env var ANDROID_UNPACK to target a folder /data/data/<app>/files and for sdl2 that + /app to get libpymodules.so

[KeyWeeUsr]

@brussee If you can, please review the new variable in the service_only bootstrap. I'm not sure if I got it right.

[inclement]

Looks good, but I'll try some test builds before merging.

Would you mind also changing ANDROID_UNPACK to something like androidUnpack in the java code parts of the service_only bootstrap? It seems like that would match the java style better.

[inclement]

I think this may have some problems with the python3 build, so I've temporarily reverted the change to custom-loader.patch to use ANDROID_APP_PATH instead (so that everything except the launcher works).

[kollivier]

Has anyone tested the webview backend since the revert? I've cleaned everything, made sure the reverted code is in my tree, and rebuilt, but I'm still getting the 'module is 0 bytes' error when building a pretty simple app with webview. (I'm building with pyjnius and android modules)

[inclement]

All merged, with a couple of other fixes! Thanks again KeyWeeUsr, I'm ashamed for the long time taken to pull it all together :<

These changes now mean that all the primary bootstraps seem to work for me.