Fix bugs

- Draw map overlay only after map is drawn to avoid duplicate overlays
- Disable map tabs and switch to info tab if a zip code search failed
- Fully clear the info tab when starting a new search
Tweak New Zap button style

make the look and feel a bit more consistent with the other button
tweak new zap button again

even more consistent with other buttons on the page
refactor code

combine global vars into a single namespace "zip"