Dassh plot input update
Update the structure of the colorbar fields in the DASSH plotting input.
Summary of changes:
- Updated the templates to reflect the proper input structure
- Updated the schema so that the colorbar{...} input is optional and each of the arguments inside it are also optional
- Updated the prechecks and input processing in PyDASSH to account for this change
- Updated the unit tests
- Updated the tutorial and its README