metadata: Add Decred Address Scanner.
Adds Decred Address Scanner to the repo. I have tested building with fdroid and seems to work. I believe all of my dependencies are open source.
$ fdroid lint com.joegruff.decredaddressscanner
com.joegruff.decredaddressscanner: Unexpected license tag "BlueOak-1.0.0"! Only use FSF or OSI approved tags from https://spdx.org/license-list
Is my license not good enough? I must change in order to be added?