Use a simpler default instance.center for tests

Point(0, 0) makes it easier to write tests with simple mental
math. For example, it's easy to tell that (2, 2) is further from (0,
0) than (1, 1) so the tests are more readable.
Factor out reusable logic in BoundaryViewTest
Add a junction table for instances and boundaries
Add a view for boundary name autocomplete
Modify boundary_autocomplete view to accept param

The user can pass in a maximum return value to override the default
of 10.
Change return type of boundary_autocomplete

Return a list of dicts instead of a list of names.
Refactor BoundaryViewTest class to support more tests
Add test for boundary_autocomplete max_length param
Merge pull request #42 from steventlamb/topic/boundary_autocomplete

Topic/boundary autocomplete