applets/kickoff: adjust visual density

This rebalances a few elements in Kickoff's UI, changing the perceived density without actually substantially changing the region elements consume on-screen.

The changes in total are:

• removing the icons in the categories sidebar. They convey little information, as they are accompanied by textual labels. What they do serve to do in the old design is to add more useless UI elements and have low spacing between them (the distance between icons is about ~10 pixels, give or take). This contributes to the crowded perception of the UI, both by adding useless elements and by having those elements be close and large from a graphic design perspective.
• smaller user real-name text; the jumbo text here crowds the text label against the top and bottom of the header, and often runs into the separator, giving the perception of a crowded design.
• a few extra pixels of vertical padding in the header and footer give the design more room to breathe, while only increasing the height of kickoff by less than 20 pixels on typical setups.

before:

after: