Add 'alert' module

[#43484231]

Simple module providing way to communicate errors to user.
It just uses 'alert' for now, but in the future, it will be easy
to replace it with another solution.
Catch and display errors while processing components definitions

[#43484231]
Add initial components-metadata file

[#43484231]

For now, only buttons and checkboxes have defined metadata.
Work in progress.
Validate button and checkbox definitions using metadata

[#43484231]