Add a Ring conformation choice to the GAG builder on glycam.org

**Is your feature request related to a problem? Please describe.**
The old gag builder on legacy is able to create the various ring forms of DIdoAp. After the user clicks on an algycone to finish the sequence you get a Ring Conf(conformation) option:
After clicking on Ring Conf, you can only pick DIdoAp residues. This is what we want.
Then after clicking on one you get a menu for 1C4, 4C1 or 2SO. If you click on one of these it alters the sequence like so(note that I edited two residues here:

**Describe the solution you'd like**
We should add this ability to the new one at glycam.org/gag. The functionality to handle this at the gmml level exists in the juggle_testBranchFreeze branch of gmml. So once that's merged into gmml-test it should all work.

Bonus: Before you click to select an algycone there is no indication that you can manipulate the ring form, so making that easier/clearer would be nice. When the user clicks on IdoA it might be nice if a ring conf box appears that they can optionally click on and inject the e.g. (2SO) into the string.

**Extra info**
In the near term future (~years) we won't want to do this for residues other than IdoA, but this may get applied to some other residues at some point.