"working" export

- create unique path per-export
- copy image data to export path
- check error codes on path/file creation
add SSZipArchive

- Add SSZipArchive
- Zip contents of export directory
- Return string of new file path to zip caller
change file name from event to guestbook
Share zip with email

- Show mail compose view with zip data
- Disable share button if unable to send email
- Delete file after compose
update readme
Merge branch 'package_export' into develop