add free-text search terms field to unified interface

[wdn5e-virginia-edu]

• simply allow advanced users to enter general query logic, including AND, OR, NOT, and ( ) grouping.
• control can be hidden from basic users until opt-in.
• other controls will continue with their current interpretation
• if other controls are left blank, this new control is the exclusive query specification
• otherwise, contents of this new control will be ANDed to other controls
• certain SQL verbs may be filtered out at the server as a security precaution
• to prevent harming database, denial-of-service attack, etc.