The client guarantees that unsupported kinds will be handled, and in
practice some clients, such as Sublime's LSP plugin, use
`"codeActionKind":{"valueSet":[]}`, since they support all kinds anyway.
This behaviour was also clarified in a [spec issue
report](https://github.com/Microsoft/language-server-protocol/issues/620)
where it was confirmed the server can send any actions it wants. It
seems preferable to ignore it.
Request types should always have the suffix Request and notifications
should end with Notification.
Also moved all request and notification types into separate folders to
reduce the number of files in the LanguageServerProtocol folder.
