fix(network, DHT): stricter typing for event listeners in interfaces

[juslesan]

Summary

Stricter listener typing for events in the ITransport and Layer1Node interfaces.

It is no longer possible to set a listener with an inproper listener function for example:
layer1Node.on('manualRejoinRequired', (peerDescriptor: PeerDescriptor) => {})
will now be caught by the compiler.

Changes

• DhtNode no longer export an Events type. It now only exports a DhtNodeEvents type that includes DhtNode and ITransport specific events.

[teogeb]

Why do the on, off and once types need to be defined multiple times per function type.

This is no longer an issue, could remove it from the "Future improvements" list

[teogeb]

This give bit strange error messages:

e.g.

const emitter: Layer1Node = {} as any
emitter.on('manualRejoinRequired', (foo: any) => {})

No overload matches this call.
  The last overload gave the following error.
    Argument of type '"manualRejoinRequired"' is not assignable to parameter of type '"ringContactRemoved"'.ts(2769)

Maybe good to add a bullet point about that into the "Future improvements" section

[juslesan]

This seems weird but I believe this is just overloading errors are reported in this case, as the assigned listener has any type in the first parameter.