Refactor query determination

[mthmulders]

The code that decides whether/how to query Maven Central is brittle and hard to oversee. It should be refactored to become simpler, better testable and easier to understand.

[mthmulders]

I believe (although I have no evidence for it) that the brittleness of that code (SearchCommandHandler to be more precise) might also be the root cause for the fact that errors sometimes get reported in strange ways, as observed in #394:

MCS ran into an error: failure: failure: failure: failure: failure: failure: failure: