Strict verification of resource deletion in TemporaryFolder rule

PR that adds support of strict verification of deleted resources when using `TemporaryFolder` rule #1001
@marcphilipp I'm confused. You are the one who suggested having `TemporaryFolder.strictlyVerifyingDeletions()`. Were you suggesting that calling that method would create a new `TemporaryFolder` instance, or have you decided that we shouldn't have `strictlyVerifyingDeletions()` and instead use a builder?