Improve workflow for changing the identity used for one's own mapping

[stefandesu]

This issue is hard to describe. Considering the following example:

• You save a mapping using identity A.
• You switch your identity to B and decide to use identity B for all mappings from now on.
• On the created mapping, it will show the yellow exclamation mark that the identity is different from the currently selected one.
• You edit that mapping, but at that moment, it will be shown as unchanged, therefore you won't be able to save it with the new identity B.
• To be able to save it, you have to switch your identity back and forth while the mapping is being edited.

Instead, it should be a two-click workflow: You see the exclamation mark, you click edit, you click save.

[stefandesu]

This was already intended, it just wasn't working when no scheme on either side was selected because MappingEditor got unmounted and remounted which caused the creator to not update properly. Fixed by updating the creator in MappingEditor's mounted call.