Removed a layer of app manager template hierarchy

[orangejenny]

Technical Summary

This is the template hierarchy in app manager that descends from apps_base.html, which is the template that sets up the left-hand menu of the app's modules & forms (and various other UI infrastructure):

apps_base.html
    no_longer_supported.html
    import_app.html
    managed_app.html
        form_designer.html
        app_view.html
            app_view_settings.html
            app_view_release_manager.html
        module_view.html
            module_view_advanced.html
        module_view_report.html
        form_view.html

This PR removes no_longer_supported.html and import_app.html from this tree, since they're simple templates that don't need the app menu. That makes managed_app.html the only child of apps_base.html, so then I combine those into a single template.

For fun, I also migrated the import app page to webpack.

Safety Assurance

Safety story

These changes are fairly mehanical. The main risk is making app manager pages 500. I've smoke tested the various pages - releases, app settings, module, advanced module, report module, form settings, form edit - to verify they still load.

Automated test coverage

There are some view level tests in app manager. I doubt this change is fully covered.

QA Plan

Not requesting QA.

Rollback instructions

• This PR can be reverted after deploy with no further considerations

Labels & Review

• Risk label is set correctly
• The set of people pinged as reviewers is appropriate for the level of risk of the change

[biyeun]

nit: i generally prefer to blocktrans INSIDE of block tags like <p> and <h1> tags, as that relies on the translator to get those tags (and closing tags) correct in the translated text...

[orangejenny]

makes sense, fixed in e9065ef

[biyeun]

my nit of blocktrans inside of <p> still applies. additionally, if i remember correctly blocktrans doesn't play well with app.name type variables (e.g. properties of variables). you generally need to do something like:

<p>
  {% blocktrans with app_name=app.name app_domain=app.domain %}
    Import application <strong>{{ app_name }}</strong> from domain <strong>{{ app_domain }}</strong>?
  {% endblocktrans %}
</p>

or those values will actually show up blank when rendered (regardless of translation). resolving this is a blocker for a ✅

[orangejenny]

Huh, that's unfortunate if values get blanked out but there's no error. Updated in e9065ef

[biyeun]

typo... i think this should be apps_base.html rather than apps_base.html.html

[orangejenny]

thanks - e9065ef