Better imports

Two things have been fixed in this branch:

1. It was not understood why exactly things were working despite the lack of `from app.models import *` in `app/__init__.py`. As it turns out, it worked because another file had the required line in it. 
    
     In this branch, I've placed the `import *` line into `app/__init__.py` and replaced every instance of `import *` (outside of `__init__.py` files) in the code with more specific imports.

    This is useful for debugging and for future developers, since they know exactly which modules are available in a given file.

2. Imports now follow [PEP 8] more closely. This is a good idea since we are planning to have future programmers work on this code; the closer we keep to established conventions the easier things will be.

[PEP 8]: http://legacy.python.org/dev/peps/pep-0008/#imports