Complete implementation and tests

[curran]

The basic starting point has been created for this module. The work that remains involves adding comprehensive tests and implementing "cleanup" when the configuration changes or the injector component is destroyed.

[curran]

@spmacdonald , if you'd like to work on this, here are some tasks that remain:

• implement setting of the "box" property. This will be similar to setting the box property in chiasm-layout, but adapted to use each individual container.
• un-inject all previously injected components whenever the "containers" property updates
• un-inject all previously injected components whenever the injector component is destroyed.

TODO comments have been scattered throughout the code. I'm putting this down for now, feel free to work from this point on your own fork and send pull requests with any progress. Thanks again for volunteering to take a crack at this.