Enhancement: Use QLOT to avoid submodules

[rpgoldman]

Currently, SHOP uses git submodules to handle dependencies for the tests, but this buys stability at the cost of possibly breaking the experience for people using SHOP with a Quicklisp installation, since the dependencies they get from QL might be different from the ones we develop against and use in the regression tests.

The qlot library by supporting project-specific quicklisp installs promises that it could address this problem for us. This is very much worth investigation.