[ACA-1508] extensions: wave 1 (#480)

* initial structure scaffold

* core extensions module

* simple navbar composition

* allow using app routes instead of registered

* migrate to new navbar setup

* remove commented out tests

* populate toolbar

* evaluate expressions

* redirect to url from toolbar

* populate "open with" viewer menu

* update test setup

* experimental flag for extensions

* test fixes

* fix tests

* code improvements, order support

* improve routing management

* populate "create" menu

* extra dictionaries for spellcheck

* allow disabling extension content

* support file/folder targets for toolbar actions

* add safety check

* navigate directly

* toolbar actions for all pages

* support route data

* "experimental" flag for "create" menu extensions

* code fixes

src/app/extensions.module.ts

@@ -0,0 +1,8 @@
+import { NgModule } from '@angular/core';
+
+// Main entry point for external extensions only.
+// For any application-specific code use CoreExtensionsModule instead.
+@NgModule({
+    imports: []
+})
+export class ExtensionsModule {}