Django upgrade follow up

[atarkowska]

This is #4236 follow up PR. It fixes:

• adds TEMPLATES settings introduced in 1.8, see https://docs.djangoproject.com/en/1.8/ref/templates/upgrading/
• removes deprecated cache_choice (never used), see https://docs.djangoproject.com/en/1.8/releases/1.8/#cache-choices-option-of-modelchoicefield-and-modelmultiplechoicefield
• resolve experimenter form password order issue reported in https://trac.openmicroscopy.org/ome/ticket/13063 //cc: @pwalczysko

Testing servers: cowfish/integration and eel/merge

To test:

• check on both servers if experimenter form fields are in the right order, see Django18 upgrade #4236 (comment)
• test annotation forms (comment, tag, etc.)

[jburel]

@aleksandra-tarkowska: travis restarted

[pwalczysko]

One more ToTest: Double-check that the Save to All problem is really gone (today's testing indicates it is gone on http://eel.openmicroscopy.org/merge/webclient/?show=dataset-2401 user-1 as well as on the leica-original 56 strong MIF - all tests passed there).

[pwalczysko]

The admin form is okay on cowfish and eel.

[pwalczysko]

Save to All works in both servers and in all situations.

[pwalczysko]

Annotations in right-hand pane as expected

• cowfish
• eel
• single selection
• mulitselection

[pwalczysko]

All works except the Secret key part - to be discussed betw. @aleksandra-tarkowska and @joshmoore

[atarkowska]

as discussed with @joshmoore secret key will go to web plugin. This will happen in a separate PR to not block changes

[pwalczysko]

Experimenter fields in the right order:

• eel okay
• cowfish okay

Annotations forms single and multiselection:

• eel okay
• cowfish okay

Ready to merge.