massive change to AbstractRunner API, but now at least it is hopefully future proof and we won't have to change it in BIC ways after 4.0

introduces two new classes: Plasma::SearchContext and Plasma::SearchAction

benefits include:
- well, future proofing =)
- the ability to eventually allow runners that mutate the search
- multiple exact matches per runner
- 'executing' of informational runners (useful for, e.g., the calculator)
- being able to centralize expensive operations such a KUriFilter actions
- simplifies writing runners *dramatically*