Issue #373 - Track params and path state in the Issue model.

This way there's wayyyy less string parsing.
Issue #373 - fetchAndRenderIssues now constructs the model url.

With an option to pass it the entire thing, rather than composing
from model path and params properties. This is used when following
Link header URIs.
Issue #373 - Use new fetchAndRenderIssues machinery.
Issue #373 - Simplify updateModelParams.

Now that we just get the param state from the model, we can
update it and let fetchAndRenderIssues do the rest of the work.
Issue #373 - Remove unused jQuery.deparam dependency.