issue-3268 new files in place for dark tab style

Adds files for new dark tab style. Currently just a copy of Unified tab style.
issue 3268 dark tab bar BG

Dark tab bar actually has a dark background now, but nothing else.
issue 3268 changed tab font

Dark tab bar style now uses a monospace font in the tabs
issue-3268 Dark tabs draw right

Dark tabs and labels now draw correctly. Still need to add unfocused app and tab hover state.
issue-3268 Dark tab style looks nice now
issue-3268 Draw left tab separators
issue-3268 Removed unused code
issue-3268 Started large refactor to simplify DarkTabStyle
issue-3268 Simplifies DarkTabStyle code
issue-3268 Code style changes
issue-3268 Gradient and text color tweaks to tabs
issue-3268 More code style changes
issue-3268 Added UI/hooks for tab style
issue-3268 Actually update tab style
issue-3268 Small code cleanups
issue-3268 Make use of enum totality checking
issue-3268 Color tweaks
Add light indicator style and clean up code
Fix merge conflicts
Merge branch 'dark_tabs_light_indicator' into saikobee-issue/3268