Lazy loading support for WiseGuiTable paging

[danbim]

For tables with a lot of entries it would be important to support "lazy loading", i.e. to allow fetching only the subset (offset, amount) of entries from the backend that is currently being displayed. This reduces the load on the backend (smaller query results) and results in smaller data transfers as most of the time e.g., the historic data (old reservations) are not required.