Suggest: search solution and search project

[eugenschindler]

Currently, it's possible to right-click on a model and choose "search model". This will search for strings in the model nodes (not just root nodes like Ctrl/Cmd+N). I have had the request from several users to have the same functionality extended to solution/language and project level. That would really be helpful to make searchability of models/languages better in another dimension than "find usages".

Side note: it would be very helpful to also make searching of non-INamedConcept strings possible.