[feature request] Make app movable to SD card

I'm on a rather old smartphone with very limited flash capacity. So it would be very practical to make the app installable/movable to the external memory (SD card).

According to the documentation, there are the following options that can be defined in the manifest:

Application developers can set the field android:installLocation in the root manifest element to one of these values:
* internalOnly: Install the application on internal storage only. This will result in storage errors if the device runs low on internal storage.
* preferExternal: The android system tries to install the application on external storage. If that is full, the application is installed on internal storage.
* auto: Let the Android system decide the best install location for the application. The default system policy is to install the application on internal storage first. If the system is running low on storage, the application is then installed on external storage. 

Unfortunately the default if not specified in the manifest is internal storage only and the app cannot be moved.