This allows whitelabel versions of apps to specify built-in app repos that
have push requests accepted by default. This is useful for the case where
there is a central manager of the core apps that are installed.
https://gitlab.com/fdroid/fdroidserver/issues/177
This is a step towards supporting easy whitelabeling, using gradle flavors.
This allows the whitelabel version to set the default repos just by making
their own default_repos.xml in app/src/whitelabel/res/values. That one
will then override the built-in F-Droid one.
