Add warning when both manual and automatic input have content

[jbellik]

Current interface behavior: If there is anything in the input for "Gen input parameters / Manual / String of terminals", then use that as the input to GEN, without regard to which tab is being displayed when "Get results" is clicked. The result is that if a user puts, for example, 'a b' in the "String of terminals" field on the Manual tab, then switches to the Automatic tab without erasing that and creates a bunch of trees automatically, and then clicks "Get results", all output trees will be based on 'a b', disregarding the input trees created in the Automatic tab. This is very opaque.

This isn't a problem if syntactic trees are manually created (using the tree builder + "Add trees to analysis"), because this clears the "String of terminals" field.

Desired behavior:

• Use inputs from whichever tab is visible at the time "Get results" is clicked.
• Possibly provide a warning if there is content in both tabs when "Get results" is clicked: "Inputs were provided on both the Manual tab and the Automatic tab of Gen: Inputs. The candidate set will be created using inputs on the tab that is currently visible. Inputs that are not currently displayed will be ignored."
• important: Don't harvest the content of "String of terminals" on the Manual tab to be the 2nd argument to GEN() unless no syntactic trees are supplied on either tab.

[jbellik]

We will need some logic around the setting and/or use of pString in interface1.js. In the master branch at the moment, pString gets set on line 423.