Updates README to reflect class object syntax

Includes notes regarding support for generic models.  Only
GenericRelation fields are supported as a means for adding generic
models to the search configuration.
Change to ModelSearch.get_queryset() signature

The new signature is `get_queryset(self, request, user)`, where the `request` argument is new.  A good number of custom requirements want to build on customized GET variables in the request, the interception of which wasn't viable without some serious hackery.
Remove old file from before the project split
Autodetect the modelSelect if not provided
Removes ajax mechanisms

appsearch no longer fetches the field and operator data via ajax when
the `<select>` elements are manipulated.  Too many errors would creep
in when requests took too long, timed out, or caused race conditions
with the field and operator pickers out of sync from rapid use.

Custom templates must now activate the appsearch javascript plugin with
the new `"formChoices"` option.  To generate the appropriate data value
for the option, use the `search` context variable to call the new
`render_all_constraint_choices` function:

    $('form').appsearch({
        "formChoices": {{ search.render_all_constraint_choices }},
    });

This serves as a background data source for all the data required to
power any of the form's choices.  The data dumped into the
"formChoices" value is restricted to the same set of searchable models
shown by the permission-filtered model `<select>`.
Housekeeping

Several small code changes:

* Removes {% csrf_token %} from the default search form.  It's a GET
request, so it's not checked anyway.  This was left behind from a
legacy migration away from the old implementation.
* Adds clarifying docstrings to several methods
* Adds a debug line during registration