Start of importer app/module

Adds initial support for parsing a file and storing each row as
database entry.

This commit also demonstrates how validation could work. The base
validations check file-level restrictions such as:
  - The file must not be empty
  - The file must have a 'point x' and a 'point y' column
  - Fields present in the file but not recognized as a valid field
    are considered errors

The next stage is to do row-by-row validations.

Currently there is no front end interface (everything being checked
by running the tests)