Warn users using alert() in case of compilation errors

[kortenkamp]

It is a fatal error if CindyScript cannot be compiled, so it makes sense to emit this message through an alert() and not only on the cs- oder JavaScript-console, as the webpage will not behave as expected (or rather: it will behave not at all).

[gagern]

or rather: it will behave not at all

With static geometry and perhaps some of the scripts compiling fine, chances are that the thing looks properly initialized at first glance, making lack of response for some interaction all the more surprising. We've had such situations already.