Add ability to create new recordings

This is a work in progress because currently the time needs to be typed
into a text field in a format understood by the application. jQuery
datepicker got messy, will return to it soon.
Validate user cannot have overlapping recordings

We don't want to be pulling in tweets for the same user twice. Using the
`validates_overlap` gem, which doesn't seem too popular but it seems to do what
I need.
Fix factories to prevent overlap validation error