Add integration points to templates so additional modules can be added without overriding templates

[jchate6]

The Basic Idea here is to implement "Integration points" that would behave in a similar way to the observation facilities, with additional modules automatically being linked into reasonable locations without a TOM admin having to override a template.
Essentially this would allow a user to install a new TOM module and have links and buttons for the module automatically appear in the proper places.

This would reduce user maintenance and allow users to more easily benefit from future improvements to the TOM toolkit.

Obvious Integration points:

• Target Detail Buttons
• Target Detail Tabs
• Nav Bar
• Target List Filters

With respect to Target Detail Tabs:

• this should include general infrastructure for this beyond the fixes in PR update redirects to target_detail page #819.
• For example, the tab names probably shouldn't be literals in the code.
• we might also consider that, as Tabs proliferate, the TargetDetail page might need a bit of a redesign

[phycodurus]

For a general overview of the strategy, please see PR #941, especially commits:

1. f1974f3
2. 00d0cb2
3. e1d7fc9
   These commits show the basic idea which is to define a TOMToolkitAppConfig that TOMToolkit INSTALLED_APPs can inherit from (it's a subclass of django.app.AppConfig). tom_base and go
   to the Django App registry and introspect the apps there looking for the extensions that
   TOMToolkitAppConfig (and it's INSTALLED_APPs subclasses) define.

[jchate6]

TOMToolkit/tom_demoapp#1 Should include information about these integration points.