After this commit, users who have the `python` executable as Python 2 can do simply:
cd android/
./build-all.py
./build.py
Previously, the following would fail:
python3 build-all.py
since build-all.py did subcalls to `python build.py`.
Remove install-all.py as it is redundant with `build-all.py -deploy`,
instead of fixing it as well.
Introduce argparse since we are separating argument parsing out of
the `main()` function.
Tested in Ubuntu 16.04, behaviour should be unchanged for Windows.
