Constraints only enforced on saving

[cochrane]

At various points in the file format, there are constraints defined (value must be more than or less than) that the UI does not actually properly enforce. That leads to the situation where everything works fine until you try to save things, when it suddenly fails, sometimes. I'm not sure which ones they are, so maybe I should just relax all of them (or at least those that have no real value, i.e. angle limitations).