Add global config

[cscully-allison]

Added a global configuration manager.

Features added:

1. A configuration manager class
   a. Basically a dictionary we can validate input on and format output
2. A validation class which performs basic type validation but can be extended to support arbitrary validation
   a. This class does require maintenance. When we add a new configuration we need to assign a validation function to the configuration key.
3. A configuration file: hatchetrc.yaml in the base directory
   a. This is loaded by default when users do not have their own hatchetrc.yaml file in directory $HOME/.config/hatchet/
   b. This is a .yaml file and accordingly should conform to the YAML syntax and requirements; here is a tutorial with an overview of such syntax: https://www.cloudbees.com/blog/yaml-tutorial-everything-you-need-get-started/
4. A global variable at hatchet root level scope: RcParams pointing to an instance of this class, it can be used in the following way:

import hatchet as ht
ht.RcParams["invert_colormap"] = True