Strict verification of resource deletion in TemporaryFolder rule

PR that adds support of strict verification of deleted resources when using `TemporaryFolder` rule #1001
IMHO, if we have this method, then we must have the rule throw an `IllegalStateException` if `assureDeletion()` is called after `after()` is called (i.e. `assureDeletion()` method is called after `TemporaryFolder` tries to delete the folder and potentially fails)