Replace the outdated list of dpkg triggers with an autogenerated one.

Signed-off-by: Dan Callahan <danc@element.io>

In #75, bytecode was disabled (from a bit of FUD back in `python<2.4` days, according to dev chat), I think it's safe enough to enable it again.

Added in `__pycache__/` and `.pyc`/`.pyd` to `.gitignore`, to extra-insure compiled files don't get committed.

`Signed-off-by: Jonathan de Jong <jonathan@automatia.nl&gt;`>

Adds note about updating dh-virtualenv once we drop support for Xenial.

We can't update now, because it needs debhelper 12, while Xenial only
backports 10.

Signed-off-by: Dan Callahan <danc@element.io>

`distutils` is pretty much deprecated these days, and replaced with
`setuptools`. It's also annoying because it's you can't `pip install` it, and
it's hard to figure out which debian package we should depend on to make sure
it's there.

Since we only use it for a tiny function anyway, let's just vendor said
function into our codebase.