Add some missing console error outputs

Those are some missing console error outputs that Morrowind has but aren't there in OpenMW for some reason:

1 - "addtopic": Morrowind outputs an error if a dialogue topic doesn't exist.

2 - "removeitem": Morrowind outputs an error if an item doesn't exist, this is already implemented for "additem" btw.

I was also wondering if there should be a warning or an error message for if an item doesn't actually exist in the actor's inventory?

3 - "startscript": Morrowind outputs an error if a script doesn't exist, this is logged in OpenMW btw, but there's no error output for it in the console. Btw the log message was:

[E] Failed to add global script "lair": script record not found

4 - "stopscript": Morrowind outputs an error if a script doesn't exist, OpenMW does nothing.

5 - "changeweather": a warning was implemented but it probably should be an error instead for consistency.

Some examples from Morrowind: