Refact map architecture to allow switching between OSM and Google maps via gradle.properties configuration

[xumeng367]

How To Use
gradle.properties
#maptype: google_map/osm
org.gradle.project.map=osm

Personal Note
Hi, and thank you for maintaining this excellent project.

I am currently working on a UAV (drone) project involving Remote ID, wireless
scanning, message parsing, and map-based visualization of aircraft state data.
Your OpenDroneID receiver project has been extremely helpful in my work and has
greatly accelerated my understanding of real-world Remote ID implementations.

I have been an Android developer for more than 13 years, and I truly appreciate
the overall architecture, code quality, and engineering practices demonstrated
in this repository.

This PR is both an improvement and a way to give back to the project. If the
changes align with your direction, I would be very happy to continue contributing.
If possible, I would love to join the project as a contributor and assist with
maintenance, refactoring, or new feature development in the future.

Thank you again for your great work and for sharing this project with the community.

[friissoren]

Sorry for the very very slow reply. I have changed jobs a couple of times lately and somewhere along the way forgot to update the email notifications from Github.

This project was the first Android application I got involved with, so my programming skills are somewhat limited in that area. If you have managed to make it possible to switch properly between using OSM and Google Maps, that would certainly be a very valuable contribution. It was one of the things that annoyed me back then, that I couldn't figure out how to do.

I have fairly limited time to dedicate to this project. I will try to setup a build environment and check your changes within the next few days.

If you really have time and interest to contribute with updates and improvements, I would greatly appreciate that. I don't know what exactly you have in mind but there are a number of open Issues that I never had the time to work on.
Probably the entire code structure is starting to get quite outdated as well (Google keeps evolving the APIs and ways of doing things).

The main purpose of developing this app originally was to assist with the very early implementation work that was done during the drone ID standardization efforts. Hence, this was never meant to be at the quality levels for a commercial app but an example that would help other people get their own drone ID implementations (transmitters and/or receivers) moving forward.

@gabrielcox: Just for your information.