Insert operation

cache_insert.scala

 def insert(key: UUID, value : Int) = {
    if (this.byKey.contains(key)){
      throw new Exception("Key already exists")
    }

    val freqNode = this.frequencyHead.next
    if (freqNode.value != 1){
      this.frequencyHead.next = LfuCache.getNewNode(this.frequencyHead, freqNode)
      this.byKey(key) = LfuItem(this.frequencyHead.next, value, key)
      this.frequencyHead.next.items += this.byKey(key)
    }else{
      this.byKey(key) = LfuItem(freqNode, value, key)
      freqNode.items += this.byKey(key)
    }
}