More frontend features and experiments

FE:
- Added some images for use on the home page. Likely not too permanent.
- Removed the sidebar from the main application display. The sidebar is
only now visible on user profiles to host Micropulses. These will soon
be restricted to only showing the user's micropulses (instead of
everyone's).
- Added the Pulsar API Error(s) console. Lots of fun Angular and CSS
going on in that thing.
- Added the .pulsar-dialog and .pulsar-layer classes
- Added styling for the <section> element. Currently only used on the
home page, will expose soon to Composer for general use in pulses.