grid generation

[smnorris]

Remove arcpy requirement for generation of grid.

Using this as a guide, refactor 01_grid_generation.

There are a few steps to this:

• consider and confirm fiona and postgres requirements
• if they are required:
  • provide shell script for testing installation of fiona on windows
  • update pgdb requirement, replacing with https://github.com/smnorris/pgdata/tree/master/pgdata or add some functions from this module to gcbm_preprocessing
• consider adding requirements.txt and setup.py to help with installation

[smnorris]

Closed with creation of https://github.com/smnorris/gcbm_preprocessing/blob/dearc/01_grid_generation/sql/ST_Fishnet.sql

Rather than dealing with installation of fiona on windows use ST_Fishnet.sql function. It is easier processing the subsequent gridding in postgres anyway.