Add tests for Tag-related components

[Chalarangelo]

Tagging functionality is not fully tested. Here's what we need to test:

Tag

• Renders correctly
• Uses given tag styles/colors
• When passed onDelete > Renders correctly
• When passed onDelete > Calls onDelete when clicked

Popover

• Renders correctly
• Renders closed by default
• When clicked > Renders open
• When clicked > Displays passed children
• When clicked > Renders closed when user clicks outside

TagPanel

• Renders correctly
• Renders given tags
• When editing a tag > calls setTagName on name change
• When editing a tag > calls setTagColor on color change
• When adding a new tag > calls createTag on submit