Batch update icon styles

Updating icon styles per gitlab-design#557 (closed). This updates the icon itself within the same 16px grid as current, and does not change naming.

Before	After

Closes #55 (closed), #56 (closed), #57 (closed), #58 (closed), #59 (closed), #60 (closed), #61 (closed), #62 (closed), #62 (closed), #64 (closed), #65 (closed), #66 (closed), #67 (closed), #68 (closed), #69 (closed)