Fixed toString method for Dictionary causing problems debugging when student iterator is not working
Fixed case "PART" should be case "QUIT" since the message that comes from the server is "QUIT" when someone quits the server.

A squash of:
AVLTree wording clarification
Update TopKSortTests.java
Bump up heap size in Gradle tests (thanks Marcus)
Fix various bugs with uMessage connection (thanks Zeynel)