Add an ALEStopLSP command to stop all language servers that match a
given name. Completions are available for the command. This makes it
possible to keep other language servers running other than the one
you're interested in stopping.
A new function is added here which will later be modified for public use
in linter and fixer callbacks. All linting and fixing now goes through
this new function, to prove that it works in all cases.
