Enhance builder

[mlewand]

This actually strongly depends on the outcome of tickets:

• Separating tests meta-data from the testing engine code #270 Review on a11y tests directory structure #269
  Since these tasks will modify directory structure, so there's reason to start builder without these issues ready.
• Extract KING Tests #364
  Because it might make sense to accept extra path as an cli argument for grunt build task e.g. grunt build --tests="/var/workspace/quail/customTests". Then it might simply include tests given in a specified directory.

[jessebeach]

Covered by: #365, #368