[webUI] Import/Export configuration

[kvndrsslr]

Please implement the ability to import a configuration in TTL format.

• The webUI should have a button "Import configuration" above or below the graph view.
• On click, the user should be prompted to select a file from their hard drive.
• The selected file should be parsed and the parsed configuration graph displayed on screen.
• In case the graph view was not empty, prompt the user if it should be overwritten

Please implement the ability to just export the configuration in TTL format without running it.

• The webUI should have a button "export configuration" above or below the graph view.
• On click, the configuration should be generated from the current model state and should be submitted to the user as a file download

[pskLana]

The general idea of importing configuration is implemented. Todos:

• [x] In case the graph view was not empty, prompt the user if it should be overwritten

• [ ] Testing

[pskLana]

Tested on demo.ttl. Nodes and properties are added correctly. However, according to the SHACL scheme obtained from the server, the current maximum number of predicates in selector is 1, therefore the UI shows this error to the user.