PCUI Examples

[willeastcott]

Added a set of simple examples for PCUI. Examples are:

• Minimal. Examples average about 50 lines each.
• Single page. No external dependencies beyond loading PCUI from unpkg.com.
• ES Module-based. Modern JS with ES Modules and Import Maps. No need for a build step using Rollup/Webpack/etc.

I've also added a basic index.html which uses PCUI to create a simple examples browser type application:

For PCUI developers, the examples are good for:

• Debugging/developing individual elements/modules. By default, examples load the last NPM release of PCUI (via unpkg.com). To run against a local PCUI build, simply edit the import maps to relative paths.
• Sanity checking PCUI before generating a new release.

[willeastcott]

@slimbuck I know the duplication isn't ideal, but a developer can open any example and see how everything works straight away. No jumping between css/js/html files. At first, I did have the css in a common.css file but I moved it back into the html files. If you contrast this with the PlayCanvas Engine Examples Browser, there it's not obvious how to set up a project from scratch. Here, nothing is hidden and I kind of really like that. But totally open to debate on this as there's definitely no solution that is perfect. 😄