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
**Notes**
* invalid state for string would be the empty string in the input field. Additional cases of invalid states would later be for example date inputs that are not valid dates.
* when clicking save the entire modal should be disabled until the modal is either closed (after a successful save) or not closed because of an error (which would then lead to an error message). This will probably be a separate story though