Markdown editor SimpleMCE is unmaintained

[nrdvana]

SimpleMDE is a great editor, but has some bugs (258 github issues), and hasn't received a commit since 2016.

There are 1000 forks, but EasyMDE looks like where all the attention went. It is getting regular maintenance and releases, and under the same MIT license. We should find out if EasyMDE can be a drop-in replacement, and if so, upgrade RapidApp.