F lazy edit mode dropdowns

Summary

For #363 (closed) (https://gitlab.com/linkahead/linkahead-webui/-/issues/262). Changes the default behavior of reference properties in the edit mode such that the dropdown menus are only initialized upon manual request. The old behavior can be restored by setting the new build variable to DISABLED.

Focus

By default, the initialization of property value inputs is interrupted for reference properties. Instead, a button is added that triggers the old function on click. The button also adds a class to the property HTML element and dispatches an event, so that the value generation upon update and the file upload can work as expected.

Test Environment

1. Run the webui with BUILD_EDIT_MODE_LAZY_DROPDOWN_LOADING=DISABLED and make sure that nothing changed. Edit an entity by adding/changing/removing reference properties and lists of references and make sure everything works as before.
2. Now run the webui with BUILD_EDIT_MODE_LAZY_DROPDOWN_LOADING=ENABLED (new default). Again edit an entity with references by

• changing an unrelated property and make sure that the value of the reference properties doesn't change or vanish
• changing the value of a reference prop
• changing a reference prop to a list
• changing a list of reference to a scalar
• adding reference properties
• removing (list of) reference properties
• ... and whatever else you can come up with.

3. Also check by looking into the network communication or the server logs that the queries to fill the dropdown menu are indeed only executed after clicking on the new button.

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Check List for the Reviewer

• I understand the intent of this MR
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• Appropriate user and developer documentation (or not necessary)
• The test environment setup works and the intended behavior is reproducible in the test environment
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src/doc/tutorials/edit_mode.rst

@@ -75,6 +75,26 @@ to the corresponding area at the bottom of the Record. Properties and
 parents can be removed from the entity by clicking on the trash-can
 symbol. Note that a Record must always have at least one parent.
 
+From LinkAhead WebUI version 0.15, the default behavior for changing
+the values of reference properties has changed in that the dropdown
+menus to select possible values are not filled automatically for
+`performance reasons
+<https://gitlab.com/linkahead/linkahead-webui/-/issues/262>`_. Instead,
+you have to click on the pencil symbol to the right of the property
+you want to edit:
+
+.. image:: edit-lazy-load-dropdown.png
+   :width: 720
+   :alt: Clicking on the pencil symbol enables the editing of the
+         reference property.
+
+.. note::
+
+   The behavior of version 0.14.x and before, i.e., enable and load
+   all reference dropdowns immediatly after starting to edit the
+   entity, can be restored by starting LinkAhead with the
+   ``BUILD_EDIT_MODE_LAZY_DROPDOWN_LOADING = DISABLED`` option.
+
 When many Entities are valid candidates for a reference property not all
 might be available in the drop down element. In those cases, the drop down
 warns, that only a subset is shown and a new button with a pencil symbol is