Reorganize share/export UI

"Image" and "Embeddable HTML" options move to share control.
Only XML export remains, and is now accessed via a sidebar
link rather than the tab bar.
Add option to include marker in permalinks
Link to sources for bulk downloads
Remove marker and filter when closed
Recenter marker when shown
Fix textarea resizing
Tighten vertical space
Update location filter checkbox state correctly
Design adjustments to Link / HTML sharing
Add "Center map on marker" option
Fix embed