Refactor global variables.

[flekschas]

Throughout older Angular JS code some global variables are used implicitly. This is an issue because the code runs magically while the developer doesn't know why.

Observed behavior

Node relationship relies on externalStudyUuid and externalAssayUuid. Both variables are members of window.

Expected behavior

Both variables should be part of the magic global variable called djangoApp which is automatically read by Angular.

This was both variables can be used via the import of settings. E.g. settings.djangoApp.externalStudyUuid is way more meaning full. In case something breaks the developer knows at least where to look.

[mccalluc]

#995

[ngehlenborg]

Related to #2202.