Add new dimensions for PETCO and Safeco

I think the scaling factors stay the same and the home plate locations
look identical.
Update image_hp_x/y points
Push database code into a single class

Try to abstract storage of data a bit. This also will allow grouping of
database access a little bit.
Convert files to use new mlb.backend.database.DB class

The class name is stupid.
Add requirements.txt

I think this works. Let's find out.
Add lxml to requirements.txt