Refactor interface1.js

[jbellik]

This file's length and complexity are getting out of control. Let's try to split it up into at least the following files:

• interface_terminalStringGeneration.js: all the logic around generating lists of terminal strings
• interface_treeBuilder.js: code that goes with the manual tree-builder
• interface_autoStrees.js: code concerning automated generation of syntactic trees and the many parameters for that
• interface_makeTableau.js: code that actually makes the tableau, and provides warnings if there are going to be too many candidates
• interface_utilities.js: functions like closeButton(), displayError(), displayWarning(), saveAs(), and possibly others

I haven't evaluated whether some of this might be hard to disentangle; if they are, we can re-evaluate this particular division of the code.

[jbellik]

Just start with splitting up the top level functions. If you feel up to writing an updated build script, then put the interface files into a subdirectory main/interface, and update the build script to handle this subdirectory.