Allow user to add data elements

[dcheli]

Currently the only data elements that can be deidentified are those "hard coded" into the system. The idea was to establish a set of data elements to start with. The current system doesn't allow a user from the Config screen to add their won data elements.

A current work around though is to find the 'user-preference-.json' file that is created when you modify current values (on windows this is located in AppData/Roaming/DataASAP) and manually modify this file.