Improve the rest-client-flow example

[hrajchert]

For the moment the example is very raw, and it is only used for internal testing.

In order to be useful as a standalone example we could do some of the following:

• Add some bootstrap styling (like the survey example)
• Add guards to the request, so that if an invalid json is provided the error message is clearer.
• Maybe remove the json request that works for all endpoints and put specific forms for each request