I went ahead and cleaned up this topic a bit so that the most relevant information is highlighted.
Below is a summary of the current options for allowing image alignment in posts, ordered by ease of installation/use:
- MD Composer extras (theme component)
- Formatting toolbar (plugin)
- Build your own solution: Image Alignment - #19 by awesomerobot and if you want to add a toolbar button, there is an example in Image Alignment - #20 by tophee