Add more themes

[vkbo]

Summary:

This PR:

• Fixes some issues with some themes from last PR.
• Makes the default themes more consistent both with each other and with the default GUI themes.
• Updates the Tomorrow themes for consistency.
• Fixes some issues with the Tango theme and differentiates it a little from Tomorrow.
• Adds the Dracula theme both as a GUI theme and a syntax theme.
• Adds Snazzy Light as a new syntax theme.

Related Issue(s):

Reviewer's Checklist:

• The header of all files contain a reference to the repository license
• The overall test coverage is increased or remains the same as before
• All tests are passing
• All flake8 checks are passing and the style guide is followed
• Documentation (as docstrings) is complete and understandable
• Only files that have been actively changed are committed