Big patch with several internal changes to krunner:
-New RunnerManager class, it manages runners at high level and gives a simple API for interfaces to use.
- AbstractRunners gains description, setIgnoredTypes, ignoredTypes methods.

Now runners can specify what SearchContext::Types they are not going to process.
- SearchContext tries shared data between the original context and any local context.

It doesn't have its own completer no more.
- SearchMatch has a new type of match, CompleterMatch. Instead of using a hard coded completer in SearchContext
- Interface class on krunner has its own completer and other changes done to accomodate the above changes in libplasma.
- A new configuration option blacklist for runnermanager and krunner instead of the whitelist of krunner.