models: rename variable mpoint to location

The variable name "mpoint" isn't clear.  Rename it to "location",
taking care to change references in views as well.

Signed-off-by: YuviPanda <yuvipanda@gmail.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
models: remove redundant import

models doesn't need to be imported in models.py.

Signed-off-by: YuviPanda <yuvipanda@gmail.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
CONTRIBUTING: add guidelines for contributing