Merge ceno-fdroid into ceno

This merge request makes a number of changes to the CENO repository to make it compatible with the F-Droid build system. This is related #17 (closed).
Some changes of note include:

• Un-patched submodules have been removed (i.e. android-components and gecko-dev). The building and publishing of these is being moved to mozilla-build-scripts. Temporarily, for development, it will be necessary to manually clone our fork of android-components. Soon, we will add building and publishing of a-c (now stored in firefox-android) to the mozilla-build-scripts repo. Once geckoview and the engine-gecko component are published to our sonatype, it will be possible to build CENO locally without cloning or building any mozilla repos.
• Because the gecko-dev submodule was removed, we needed to copy the android_version_code.py script to generate our versionCodes (to keep consistent with CENO v1.6.x)
• All references to firebase have been removed, these cause F-Droid scan to fail.
• Automatic signing of release builds has been removed. F-Droid signs apks with it's own signing process, for our own builds we can sign using the cmdline tool apksigner and add that to the build script (this is how CENO v1.6.x was signed anyway).
• It adds the ouinet configuration to the source code. This must be published because F-Droid requires that the all code is 100% open-source.

Hopefully this merges smoothly without many conflicts 🤞