Added API to cancel request. Also: renamed RetrieveStolpersteine -> RetrieveStolpersteineRequest
Request data with delay so that request can be canceled when user types quickly
Revert "Removed URLEncoder.encode, because it does not make sense for whole URL (but for query parts).  Tested OK (all bio urls are only consisting of alphanumeric letters and “-“)."

This reverts commit 8ed95f5e2182a735a6a5e9c3e36ae4f63f4318db.