Add group to display multiple checkboxes as a set of icons

[RunDevelopment]

I added a new icon set group. This group will display multiple checkboxes as a set of icons (similar to the "icons" dropdown style). I used this new group in Text As Image and Color Levels.

Other changes:

• Removed explicit option labels for Alignment input of Text As Image, because they were the same as the auto-generated ones.
• Slightly change/refactor our *Label components to make the optional prop optional.
• Fixed text icons not inheriting the cursor from their parent elements.