Additional style updates

[Pjb518]

A third round of style updates to standardise the naming system, remove old style declarations, and simplify the overall implementation.

• [x] Unify the sheet classes to remove code duplication
• [x] Simplify the settings classes
• [x] Create a dedicated radio button component
• [x] Add binding classes where they haven't already been implemented (excluding actor groups)
• [x] Make the entire toggle button clickable on the setup sheet pane
• [x] Simplify desk styles
• [x] Update all of the template styles

Update 1: The latest round of changes should complete the update to the new naming scheme, following standard BEM conventions with a handful of utility classes.

The only classes which have not been updated are those for the forthcoming actor groups feature. It's likely that only a handful of new styles will be needed over the current generic components, meaning that most of the existing front-end code for this feature will be discarded.

Update 2: The PR now includes updates for the majority of the actor group styles, as well as template changes for the actor group feature.

Update 3: The PR now also includes the preliminary work for setting custom themes. The var function is used to associate custom property names with specific system elements; however, no values for these custom properties is set. Instead, a fallback value is provided for each var, acting as the system default. Users can modify the styles by setting values for the custom property names used in the system CSS.

These additions will be built upon when we get around to implementing custom styling for the system interface.

[Pjb518]

Known issues as of the latest commit:

• ~Checkboxes are not working on the new actor groups.~ Turns out the data is updating when a checkbox is clicked, but the checkboxes themselves don't represent that change visually in the new actor group sheet.
• Actor groups currently have no help text.
• The input element for the actor group name currently does not update the name of the actor group.
• Some of the actor group classes have not been updated to the new format.