Small code refactor and fixes

This release has some minor fixes.
The code has been refactored and cleaned by @tohosaku .
Tested on Redmine 5.1.1.

Working on Redmine 5

The plugin now works on Redmine 5.
Also, upgraded the reveal.js library to the latest release.
Now you can use auto animations between slides!
Add the animate=true in the slide and subSlide macro parameters (or use the dialog) and revel.js will perform animations between slides.
See the reveal.js documentation for more details.
See the demo.textile file for an example of slide definitions.

Fixed macro buttons in editor when using markdown syntax

Macro buttons in the toolbar were not displayed when using markdown syntax.