Adding new properties to sources and trees

[chinchliff]

Need to be able to add new properties to sources and trees in from the source view screen. Basically, an "add property" button should appear when in edit mode at the bottom of the table, which will add a row with a dropdown and a blank field. Set the property name in the dropdown and the value in the field and save changes to record the edits to the db. The dropdown is so we can restrict the keys to the set of approved ot: properties, but we can could allow custom properties, we just want to give people the set of known properties so they don't have to type them by hand...

This will require making property lists available via services. Need to add all the ot: properties to the enums to do this. See the nexson documentation page for the list of available properties: http://opentree.wikispaces.com/NexSON

[chinchliff]

Have begun this. More work to do on source_view.html

[chinchliff]

Making progress. Need to finish defining the presets in OTPropertyChoices and then populate the JSON map in the page using them.

[chinchliff]

This appears to be done.