Add ability to search all files in the project

Adds a "Find in Project" option to the "Project" menu and a "search" function to the ProjectManager.  Regular expression and multiline queries are supported.  Clicking a result will open the file (if not open already) and move the editor's cursor to the appropriate line and column.  I have plans to make this a combination "Find / Replace in Project".  Let me know if you have any questions.
For output, I'd like to look into opening a new tab and feeding it data, the way Sublime does, rather than coming up with a new way to present results. If you must present results, the palette already has a way to do that, and we should use that instead of coming up with a whole new output mechanism.