[bug 927617] Fix some ui issues with occurrence report

This fixes some ui issues with the report:

1. adds placeholder text for date fields with the date format
2. adds an obvious permalink since the form data is all in querystring
   to make it easier to share report urls between people
3. hides the results unless there are results
4. fixes a problem where if the date fields are malformed, then it
   throws an error
[bug 927617] Add basic tests for occurrences report