Strict verification of resource deletion in TemporaryFolder rule

PR that adds support of strict verification of deleted resources when using `TemporaryFolder` rule #1001
Although I personally prefer a Builder, we agreed to try to avoid it here. Why can't we just add a setter method in 'TemporaryFolder` named `strictlyVerifyDeletions()` that returns `this`? The method would throw `IllegalStateException` if it was called after the `before()` method was called