Remove dependence on "org.fdroid.fdroid" to make whitelabel clients easier

We encourage people to fork F-Droid and use it (according to the license) for their own "white label" app stores. Currently this is difficult because there are a bunch of places where "org.fdroid.fdroid" appears, and in more-important-than-they-should-be places.

The worst offender is FDroidProvider and its subclasses. They have an AUTHORITY which is "org.fdroid.fdroid.data". This is based on the package they belong to, and it is difficult to change because I think it needs to correspond to their package. This is also duplicated in the AndroidManifest.xml which has several <provider> elements, each specifying an android:authorities and android:name, e.g:

<provider
    android:authorities="org.fdroid.fdroid.data.AppProvider"
    android:name="org.fdroid.fdroid.data.AppProvider"
    android:exported="false"/>

Other (seemingly) problematic places which wont cause a crash straight away, but likely will cause problems down the line:

• The check in FDroidApp for "org.fdroid.fdroid:acra".
• PackageManagerCompat calling setInstallerPackageName("org.fdroid.fdroid")
• The swap related stuff treats the "org.fdroid.fdroid" package as special, always adding it to the list, and allowing it to be sent via Bluetooth.

Non-problematic (but still worthy of refactoring) places include all of the ACTION_* and EXTRA_* constants which are prefixed with "org.fdroid.fdroid". They don't need to change, because they are just dumb strings, but it is silly to require people to fork and rename the client, but leave references to F-Droid everywhere.