allow installation to external media (microSD)

[leggewie]

This change will enable installation of the app to external as well as internal flash memory which is important for devices where internal memory is limited but external memory is cheap and abundant in form of micro SD cards. Please have a look at https://developer.android.com/guide/topics/data/install-location for further information. Thank you for your consideration.

[AndreasGassmann]

I don't know anything about this feature, but looking at the docs, specifically this section here, it looks like our app should not be installed on an external media because the background services (eg. bluetooth scanning) could be stopped under some circumstances and will not be restarted again automatically.

Is it really necessary to add a feature like this when the app is only a couple of megabytes?

[leggewie]

Those circumstances are that you remove the SD card.

This change only allows the installation to SD card. The default will still be to install on internal flash. I certainly would like to have this choice.

[javirico83]

I may need more help to make sure im doing it right