Initial project system

Fixes #9 

## Remaining work

* The branch includes many unnecessary features in the project system property pages, and/or items which do not make sense for Dart projects
* ~~Need to disable the scanning, and only enable Dart analysis for non-**.dartproj** projects if/when a Dart file which is in that project gets opened~~ (#38)
* Project templates
  * [x] Identify reasonable project templates for Dart projects (**help wanted**)
  * [x] Implement the project templates
* Item templates
  * [x] Identify reasonable item templates for Dart projects (**help wanted**)
  * [x] Implement the item templates