Make it possible to ignore unavailable tools

Some of the tools we know how to test are difficult to obtain, like Near's original "bps" tool, or python-bps which needs Python know-how and a virtualenv. Alongside the "create" and "apply" scripts in the tools/ directory we should have a "detect" script that checks whether the given tool is available in the current environment, and maybe prints some information about where to obtain a copy and where to install it so it can be tested.