Avoid error when a not yet handled elements is in the source

[apupier]

for instance when there is a rest element which is not yet handled, we store the json string corresponding to it and returning it back

fixes #500

[apupier]

it requires to add tests. i think we should add for rest but also for all other elements not yet vizualized, with a specific entities, like restconfiguration, routeConfiguration

I initially thought to provide a specific identity for the rest element but it would have left apart all the other cases. So sounds safer to have a generic entity to handle all elements that we just do not want to lose but for which we are not providing a vizualization

And also need to look at all the broken tests

[lordrip]

I added a fix for the tests: apupier#1

[apupier]

I added a fix for the tests: apupier#1

I also updated the tests locally but in fact the real problem introduced is that when from without route is used, it is no more working, the from route is ignored.

[apupier]

Provided branch from Ricardo is working. i was hitting a different issue, which was already present. this issue is that routes using top-level from and which does not have a steps element (so that are incomplete route) are not displayed in the canvas. --> reported #581

So it remains to provide new tests

[lordrip]

@apupier is there something that I can lend a hand with? 😃

[apupier]

is there something that I can lend a hand with? 😃

it remains to provide new tests

EDIT: I'm on it now