Change Details

* Disable save button when nothing is changed yet or state is invalid

We don't want the user to be able to save any state of the bridge to prevent incomplete or potentially faulty edits to occur on Wikidata and to prevent a system error in advance. Therefore we have to disable the save button for some of the states. the disabled state should be `ButtonWidget (progressive, disabled)` looking like this (button in the top right corner) {F30199651} **Acceptance criteria** [] Save button is disabled when nothing has been changed yet [] Save button is disabled when state is invalid [] Save button is disabled when value has been changed but none of the radio buttons have been selected yet (this is NOT true for when only a reference has been added/edited) **Notes** * is it possible to know whether the phone/computer currently has an internet connection?