Bugfixes

[alukach]

A collection of small fixes:

• Normalize the format of API endpoints used throughout the codebase. These endpoints are added to cadasta.common.setting.get_url_instance(). It was ambitious is get_url_instance() returned a URL that ended with a trailing slash (/). It appeared that some API requests were being made to https://host//..., where two slashes existed between the URL base and the endpoint. Instead, we'll ensure that get_url_instance() does not end in a trailing slash and expect that all API endpoints begin with a slash.
• Fix bug around handling paginated GeoJSON
• Update parties and relationships API requests to expect paginated responses
• Remove unused imports

[alukach]

I'm just going to go ahead and merge these into my paginated-support branch