Update plugins.json

Add AEFlowchart plugin
Merge pull request #3 from tadija/patch-1

Update plugins.json
Small fix for description for AEFlowchart
Add dedicated CONTRIBUTING file

via https://github.com/blog/1184-contributing-guidelines
Add Color Contrast Analyser plugin
Add Page Switch Plugin
Merge pull request #4 from mauehara/page-switch-plugin

Add Page Switch Plugin
Added Sync Plugins
Added New Plugins
Merge pull request #6 from NathanRutzky/master

Added New Plugins
Added Generate Animated GIF
Update plugins.json
Merge pull request #7 from NathanRutzky/master

Added Generate Animated GIF