[FEAT] Handle bpmn-visualization load errors in examples

[tbouffard]

Update the examples loading external BPMN source

• bpmn-vendors comparison: open a window alert as when using bpmn-js
• load local diagram: open a window alert
• load remote diagram: display BPMN load success or error in a dedicated
  status area

In addition, for the 'load remote diagram' example

• round fetch and load on Chromium
• display duration in the status area on fetch ko

closes #281

Implementation notes

This Pull Request initially includes a bpmn-visualization development version which did no longer open a window alert. A revert commit is included in the later changelog as a released version of bpmn-visualization (0.21.3) is now available with this change.

Live environment of examples

https://cdn.statically.io/gh/process-analytics/bpmn-visualization-examples/281-manage_bpmn-visu_load_errors/examples/index.html

Design change in the 'load remote diagram' example

Show the 'load status' area

bpmn-remote-load_status.mp4

Duration on fetch ko

[tbouffard]

@csouchet we can change the color of the background for a sucessfull load. What do you prefer?
We can also introduce our own toast-load class to use a dedicated background color

2051985	without the toast-primary class

[csouchet]

@csouchet we can change the color of the background for a sucessfull load. What do you prefer? We can also introduce our own toast-load class to use a dedicated background color
2051985 without the toast-primary class

@tbouffard

I don't like the primary color for the Ok message. There is too many elements with this color.

ℹ️ Also, generally, the container message is used for the error and not when it's ok.
I'm not sure that is very useful to have the 2 OK messages when all is well 😕

[tbouffard]

Final decision: keep the 2 status area for now (we need to merge this PR to handle load errors. Improvement can be done later). The load status is filled in green on success.