Add multi statement query warning when multi statement is disabled

[HerrEmil]

When the editor checks the current query with explain, the potential mistake of sending multiple statements in one query is not caught. Frontend has the info to flag this issue so this PR adds an extra check on editor update, and displays the warning as a warning triangle in the editor gutter.

When clicking other warnings in the editor, an explain query is sent and the result displayed in a warning frame. Since this warning is caught in frontend, that query is skipped and a simple error frame with a message is displayed.

[OskarDamkjaer]

Nice little video! I get this though..

It sticks even when I remove the query and clear the local storage.

I'll try to see if i can find what went wrong

[OskarDamkjaer]

I think it'd be really nice if the warning went away automatically when the box got ticked, not sure if out of scope though :)

[HerrEmil]

Nice little video! I get this though..

It sticks even when I remove the query and clear the local storage.

I'll try to see if i can find what went wrong

Thanks for flagging these, both were my bad and I've found how to fix them :)

[HerrEmil]

I think it'd be really nice if the warning went away automatically when the box got ticked, not sure if out of scope though :)

I agree, I will try adding that