add new literal value to generic resource

[angelo-v]

As a Pod owner I want to add new properties with literal values to an existing resource, so that I can add information even if I do not have a specific app for this type of resource and also no knowledge about editing raw turtle.

Acceptance criteria

• [x] when viewing a generic resource I can add a new property and literal value
• [x] when typing a propery name I get proposals from common vocabularies, I can choose from
• [x] I can also insert a URI that is not in the proposal lis
• [x] the new property and its value shows up in the list of literals
• [x] the type of the value is a simple string
• [x] show an error message, when the resources could not be edited
• [x] do not provide this feature when the document cannot be edited by the current user / visitor

Out of scope

• other data types than string
• adding links / relations to other resources
• languages of literals
• if the property is relative, it will create a URI relative to the current document

[angelo-v]

Technical notes:

• WAC-Allow headers contain info about the access rights, but there should be a higher-level method to check it via rdflib
• there is an npm package rdf-namespaces that could be used for the autocomplete list

[angelo-v]

Open Tasks

• [x] integration tests for data input
• [x] styling
• [x] resource is not considered editable directly after login (caused by https://github.com/linkeddata/rdflib.js/issues/441)
• [x] add event for changes in pos-select-term
• [x] use selected term when saving
• [x] consider using type Term in addPropertyValue method instead of string
• [x] update literals list after adding a term
• [x] e2e test
• [x] storybook / docs
• [x] allow to add relative property uris
• [x] error handling
• [x] show error when adding property value to a container resource

Nice to have

• [ ] scroll to input after saving
• [ ] when to save? on change? on enter? what if only predicate changes?