Also fix a bug where it was possible for shops to be created with shop owners that did not have a valid Account information when other plugins manipulated the name line after the NameChecker checked it. Now it gets checked twice, once at the start (to abort early and to populate the ownerAccount field) and once at the end to check again when the name line changed.
This should fix the issue where the player's short name on the shop sign does not reflect the actual player's name. This works by storing every uuid-username combination together with the associated short name and the last time the player logged in with that combination.
