Add option to reverse the message flow

[izzy]

Adds option "Reverse Flow" in the settings which depending on the settings will change flow like following:

• Bubbles
  • Bottom-Top -> Top-Bottom
  • Right-Left -> Left Right
• No Bubbles
  • Top-Bottom -> Bottom-Top
  • Right-Left -> Left Right

[bogdan-baerov]

I wanted to suggest this until I saw this issue is already open. I can't wait for this, I would've helped here but this beats me, JS isn't my strongest suit apparently XD
Also, I wanted to ask, should I close #36 ? Since that is done from what I think.

[izzy]

I just moved this down to the 0.4.x Milestone. After the past week I realised that the code needs some substantial core changes to keep it maintainable in the long run, especially with more customization options to come.