Implement a real loop for plugins

[hlxid]

Fixes #26
Heres my test code:

import org.codeoverflow.chatoverflow.api.plugin.{PluginImpl, PluginManager}

class simpletestPlugin(manager: PluginManager) extends PluginImpl(manager) {
  loopInterval = 1000
  var startTime = 0L

  override def setup(): Unit = {
    startTime = System.currentTimeMillis()
    log("Started successfully!")
  }

  override def loop(): Unit = {
    val delta = System.currentTimeMillis() - startTime
    log(delta.toString)
    Thread.sleep(500) // fake execution time
  }

  override def shutdown(): Unit = {}
}

[sebinside]

Works fine. Thank you for your patience and the PR!