Don't change build systems automatically
Remove automatic build sys selection for pubspec
Add helpers for managing our own build system
Implement custom build system infrastructure

- We no longer use the default build system framework as the
  primary framework for building files in dart projects.
- Create a notion of a 'primary' and 'secondary' actions, mapped
  to F7 and Ctrl+F7 by default.
- Add smarter context detection so that the new build system knows
  how it should build the files.

Advantages:
- Eliminates conflicts with non-Dart build systems.
- More flexibility to perform sensible build operations.

Disadvantages:
- Temporary loss of convenience. Some features present in the
  default build systems have not been ported yet.
Fix bug; refactor
Add regexes
Merge pull request #221 from my-personal-forks/build

Replacement build system for Dart projects