Added time-based show and hide functionality to actionbar

[Fameless9]

Hi, this PR adds a hide-after and show-after option to the actionbar. The runnable controlling when to show and hide the actionbar automatically cancels when the point has finished or the hide-after has been reached, so it will not lead to any overload on the server.

Example:

Configuration:

actionbar:
  message: '&4Text'
  show-after: 2.5
  hide-after: 3.5

ServerTutorialPlus.actionbar.mp4

• by default, the text will stay on screen until the point has finished
• to hide the text when needed, an empty actionbar message will be sent
• show-after and hide-after should both be specified in seconds

[MartenM]

Changes seem fair enough. I do remember the actionbar having an option to 'repeat' though. How does it interact with that functionality?

Also I am not seeing a command that allow for editing this variable. Please attach an editor that allows for this for the corresponding points. Check how this is done for the other points.

[MartenM]

Please follow the java naming conventions (even though I messed up the message_actionBar variable).
So actionbarShowAfter and actionbarHideAfter.

[Fameless9]

Hi, the changes won't interfere with the repeatActionbar, however, the actionbar will never be hidden when repeatActionbar is true.