Examples: load BPMN content from external file

[tbouffard]

With introduction of #14, #15 and #16 , the BPMN diagrams content are inline in the javascript code which make it quite long and disturb the user code reading as we mentioned in process-analytics/bpmn-visualization-js#433.
Find a way to put the BPMN content in a file and make the examples load this BPMN file (js script loaded as module + use import directive to load the file content?)

[tbouffard]

The BPMN diagrams are now retrieved with javascript functions stored in dedicated files.

[tbouffard]

We want the examples to work without a dev server, using file browsing. So we cannot use the fetch API to retrieve the diagrams.
See https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS/Errors/CORSRequestNotHttp

If we decide to drop the local file support browsing we will be able to put the bpmn content out of the js code, in dedicated files.

[tbouffard]

This will be only implemented in project for now as we want to keep the local file support browsing.