ToDo List is XML Configurable

Closes #8 
This commit does require that the ../resources/rubberduck.config file be copies to the %AppDataLocal%\Rubberduck\ directory.

For example:
    C:\Users\UserName\AppData\Local\Rubberduck\rubberduck.config

Changes to the configuration can be made in this file by adding TodoMarker elements.
ToDoMarkers have two attributes, text and priority.

    <ToDoMarker text="'BUG:" priority="2" />