Merge branch 'recreate-cache-dir' into 'master'

Recreate cache directory after deleting app data

This fixes a warning on the Moto G:
```
E/libEGL: error creating cache file /data/data/org.briarproject/cache/com.android.opengl.shaders_cache: No such file or directory (2)
```

@grote might possibly be related to hardware rendering issues.

See merge request !326