Forms should have a set_queries method

[jace]

When a form uses QuerySelectField or QuerySelectMultipleField, it may specify either a query_factory in the form class, or a query function in the form instance. The latter is used when the query must take context into account.

As a pattern, we prefer query construction in the form itself rather than in the view (see #112). We do this by overriding __init__ and setting self.field.query after calling super. This is a bit clumsy as it masks the form's calling pattern (as using *args, **kwargs hides details from inspect). The base class's __init__ should instead call self.set_queries() and provide an empty function, which form classes can override to set queries, without needing to accept arbitrary parameters or call super.

[shreyas-satish]

Why set_queries() and not set_query()?

[jace]

Because there may be more than one query select field.

[shreyas-satish]

#148

[shreyas-satish]

#148 fixes this.