fix admin localized strings popup

[hburgund]

Some Add New ➕ signs in the django admin (such as in Project edit screen) proceed to a new page in the same browser window to add a new localized string rather than a popup. This results in a breakdown of the workflow and is very frustrating. Needs to be fixed.

Thankfully, django 1.9.12 fixes the problem, though I am not sure if that upgrade causes any other issues. There may be incompatibilities with certain external django apps etc.

All unit tests pass, but we only have 55% coverage.

[hburgund]

Django 1.9.12 doesn't fix the problem in custom templates like roundware/rw/templates/rw/tag_add_to_category_form.html. This form is quite old and I'm guessing it instantiates things differently or something. The plus sign is still there, just doesn't do the popup like it should.