Added Javacord as a compliant library

[Bastian]

This pull request (re)adds Javacord as a compliant library. The library got removed (commit discord@c4a4783), because it didn't properly handle ratelimits (see discord#108) back then due to not being actively maintained.
The latest version is a complete rewrite which properly handles ratelimits (delay actions using the headers to not cause 429s) and is 100% feature-complete besides voice.
These are the ratelimit-relavant classes, if you want to check:

• RatelimitManager.java
• RatelimitBucket.java
• RestRequest.java

The result would look like this without hitting any ratelimits:

for (int i = 1; i <= 12; i++) {
    channel.sendMessage("Ratelimit Example #" + i);
}