Breaks multiple values in date fields into separate lines #583.

[bwatson78]

1. additional_catalog_helper.rb: abstracts away the test and processing for making dates fall on multiple lines.
2. _about_this_collection_block.html.erb and _metadata_block.html.erb: adds a switch to the separate line processor if a date field is detected.
3. additional_catalog_helper_spec.rb: creates a test suite for the helpers used here and previously.

[bwatson78]