ReactButton 2.0.0

• Support a dynamic number of reactions
• move icons to example app to reduce the library size
• support to split the reactions into multi-columns
• move reactions dialog from the centre to dynamic position depend on the button position
• provide 2 listeners to listen for dialog state and reaction change
• handle dialog position when the device rotates
• improve code and comments
• add examples in the example app
• Update Gradle version and compile SDK version
• update readme doc and examples