Bug: Validator does not change mode back after validating a Dataset Site

[nickevansuk]

Journey:

1. User validates a Dataset Site URL
2. User then validates an RPDE feed

At step 2 the validator remains in Dataset Site validation mode, confusing the user. The validator should auto-detect the RPDE feed and change the mode back to RPDE if it is not already either RPDE, Bookable RPDE, Orders RPDE or OrderProposals RPDE.