New localgov date formats are missing UUID when installed during an update

[andybroomfield]

Follow up to #72
If the new core.date_format.localgov_forms_date_datetime and core.date_format.localgov_forms_date_short_date where installed via an update hook, they will be missing a UUID (its set to NULL). This can cause a deployment issue in certian environments that check for config diferences after the deployment (like Acquia BLT).

We need to write an update hook to add the missing UUID for those who don't add it manually, checking not to replace the existing one (those who install the module instead of updating will have a UUID already).