Add 'add all' buttons to column sections and groups

These are cosmetic only, they are not connected to any handlers at the
moment.
Add descriptive class names to buttons for improved selectors
Add handler for adding all section and group items

This commit also prevents duplicate concepts from being added to the selected list
Add a remove all button to the columns modal
Add option for toggling section and group "add all" buttons
Adjust style to align buttons and add more spacing
Merge pull request #159 from cbmi/issue-158

Restore "add all" and add "remove all" functionality