Where it makes sense, allow plug-ins to define their order relative to
other well-known plug-ins within the system, rather than hard-coding
this information within the model (see #386).
Only produce each plug-in list once during construction, since they
never change later.
Removed redundant TODO.
Make the code more re-factorable by generating the class names, rather
than hard-coding them.
Initialize the model before creating the command, as this was preventing
this test being run in isolation, which was (for some reason) causing
the Travis build to fail.
Merge pull request #461 from BladeRunnerJS/ordered-plugin-support

Where it makes sense, allow plug-ins to define their order relative to