* Remove `work_package_id` column from time & cost entry

* Mark new entity fields as not-null

* Begin of the insertion~~Remove~~ `~~work_package~~` ~~fromEnd of the insertion Begin of the deletion Remove `work_package` fromEnd of the deletion the API and require it to go Begin of the insertionthrough~~ `~~entity~~`~~.~~ API changes are postponed to 19.0 (<mention class="mention" data-id="79926" data-type="work_package" data-text="##OP-20189" data-display-id="OP-20189">##OP-20189</mention>)End of the insertion Begin of the deletion through `entity`.End of the deletion