Editing constraint logic

When adding constraints to a query, an expression is now automatically generated to describe the logical relationship between the constraints. The existing webapp ANDs all constraints together. By default, the new webapp will do the same until the user intervenes, either by changing the default operator for new constraints (from AND to OR) or by editing the logical expression directly.

When updating the expression, the webapp will try to fix any problems. For example, it will add unmentioned constraints to the expression and remove unknown ones. It will also remove unnecessary brackets.