Add `DEBUG` option to external C dependencies

for issue #85

fixed crash when an user tries to add the same hidden service port twice

- add new flavordimension tag

This patch allows the developer to build the external binaries with
DEBUG=1 which ensures that the final binaries are not stripped from any
debug symbols.

This makes the binaries useful together with Google's simpleperf
profiler for Android.

Because of bug #90 the current build process will be broken for people
who have Zstandard headers available on their host system. For people
who do not have the headers available the build system will silently
ignore the `--enable-zstd` and build Tor without support for it.

See: https://github.com/n8fr8/orbot/issues/90

in lite of the feature enhancements and new version of tor

- also make app selection more streamlining

update gradle depends