Code review comment for lp:~widelands-dev/widelands/workarea-fixes

As pointed out by hessenfarmer in https://bugs.launchpad.net/widelands/+bug/1830345/comments/17, The beekeeper would be interested in farms and berries too. So, let's keep the Lua design and add those to the building. A rule-based approach would get very complicated with that.