Add "Dracula" application theme

Description

This adds a "Dracula" styled application theme, mainly for Windows and Mac systems, where themes included in the source are used, instead of the ones supplied by the OS.

Together with the already included worksheet theme, this themes all aspects that a regular user comes into contact with. Color maps are still pending (implementation as well as discussion about actually implementing)

Choosing the theme for testing:

Conformity

• Changelog entry
• Downport
• Unittests