Create different search contributors for the global search

[lmihalkovic]

The global search in #4077 should be extensible. At the moment there are 3 default contributors. It would be interesting to know what kind of information people would like to have.

Possible examples:

• list of tutorials available on arduino,cc (keyword "tutorials"). Selecting one should directly open the matching page. Would be nice if the company would have a json file somewhere with that list, instead of having to do some scraping
• list of boards ( keyword "boards"). Again, selecting an element should open a official description page
• list of events.. a quick way to access a list of sanctioned events registered with arduino.cc

The list of possibilities is endless...

[ffissore]

Since the feature doesn't yet exist, it doesn't make much sense opening another issue for saying what else it should do. Please keep the conversation going in #4077

[lmihalkovic]

[LMDONE]