Since the two executables are really contentless, we can directly
invoque the python interpreter for the bridge and erebor. This still
assume that this is installed on each computer of the infrastructure.

Use the binaries to make sure that the imports work. There's probably
still some weird things in there, but it's a start.

This is the somewhat standard python package source organization, should
make it easier later on.

Paths are not updated in this commit, meaning that most imports will
probably fail.