start-gs: record non-transparent

Record with a black background (I have pseudo-transparency set in my
`.Xresources` -- `+tr` negates it).
add latest Edmodo submission & ttyrec
fix submission GitHub link
Make version info an option; add main repo mode

Bah, version info doesn't matter with Java. I might change it up later,
but for now, it's only GCC and it's an option.

`-o` triggers 'aqa-computing' mode, which means your work is in main
repo `aqa-computing` rather than its own repo. The latter has become
default behaviour for me, so it's been depromoted to an option. What it
does is simply rewrite the GitHub URL to work for subdirectories (to a
very limited extent).
fix submission.md links
move teststore->testStore :>