Clicking the menu chevron should expand/collapse the menu

[chris-lawton]

Issue Summary

Currently each list of patterns in the left hand menu can be expanded and collapsed via clicking the title e.g. 'Components'.

Next to the title is a chevron icon that when clicked should also expand and collapse the menu.

If this was not the intention then cursor: pointer should be removed when hovering the icon.

Steps to Reproduce

1. Go to a pattern library
2. Click the chevron icon next to a list of patterns in the left hand menu
3. Menu should expand but does not