Interaction response

[felldo]

This implements the ability to respond to interactions.
Also fixed a hard coded limit for webhook embeds in the message builder.

Internal PR implementations:

• Responding to an interaction
• Followup messages

Issue implementations:

• Respond to application commands

Usage example:
The most basic response to receiving an interaction is by simply sending your initial response.

api.addInteractionCreateListener(event -> {
    //Both are the same
    event.respond().setContent("Initial Response").sendInitialResponse(event.getInteraction());
    new InteractionMessageBuilder().setContent("Initial Response").sendInitialResponse(event.getInteraction());
    //Delete your initial response
    event.deleteInitialResponse();
});

You can also hide your response from other user with setting the EPHEMERAL flag for the message

api.addInteractionCreateListener(event -> {
    event.respond().setContent("Initial Response").setFlag(Flag.EPHEMERAL).sendInitialResponse(event.getInteraction());
});

It's also possible to respond to an interaction later but for a maximum of 15 minutes after the first time you have answered to an interaction with your first response or through #respondLater()

api.addInteractionCreateListener(event -> {
    event.respondLater().thenAccept(unused -> {
        //Edit your original response. In this case you edit the "loading state" response
        new InteractionMessageBuilder().setContent("Deferred Response").editOriginalResponse(event.getInteraction());
        //
        //... 5minutes later
        //
        new InteractionMessageBuilder().setContent("Followup Message").sendFollowupMessage(event.getInteraction()).thenAccept(message -> {
            new InteractionMessageBuilder().setContent("Edited followup message").editFollowupMessage(event.getInteraction(), message.getId());
        });
    });
});

[felldo]

I am not 100% satisfied with the location of some methods like #deleteInitialResponse located in the event. It could also be moved i.e. into the Interaction class event.getInteraction().deleteInitialResponse() but I am not sure and open for suggestions.

[bassner]

Added a minor suggestion (open for discussion), otherwise this LGTM. :)