Fix a sneaky bug in handlebars helpers

 is destructive.
Update version of Shareabouts.js dependency
Add a button for requesting a new snapshot to the shareabouts settings
Merge branch 'staging' into shareabouts-download-link
Only request a new snapshot if we haven't yet.
Clean up

- Move download button markup into a template
- Move filename parsing into a handlebars helper
Merge branch 'staging' of github.com:openplans/planbox into shareabouts-download-link
style data download link/message/button
Merge pull request #97 from openplans/shareabouts-download-link

Shareabouts download link