A method in the http API to close all open websocket connections

New method `http.closeWebsockets()`
- Takes no arguments. Closes all open websocket connections

# Why?
If you have too many websockets open, even if they've all been lost out of scope, CC will cause new websockets to error. A way to close them all would be useful (for instance in a shell after all programs terminate, or in a startup file to reset the programs without rebooting. 