Add linters to deltametrics: flake8-simplify

[mcflugen]

Adds the flake8-simplify linter to sandplover and fixes some issues.

Issues fixed include:

• Multiple isinstance calls that can be merged into a single call by using a tuple as a second argument
• Use a single if statement instead of nested if statements
• Combine conditions via a logical or to prevent duplicating code
• Use key in dict instead of key in dict.keys()
• Reflexive statements (i.e. remove statements like cmap = cmap)