rework devon4j-http-rest-client tutorial

[EduardKrieger]

devon4j-http-rest-client

The tutorial wiki generation involves some changes that has to be done for the tutorials.

The name of the function nextKatacodaStep has been changed to make it clearer that there is no functional content allowed.

1. use a higher header level for Prerequisites and Learning goals.
2. use a header two level higher for the header in the step Modify properties for server configuration in the description text.
3. add a newline between To test Synchronous method, follow below steps. and the enumeration
4. Remove the useless ==== in line 217, 219 and 222 and put the explanation at 220 in a conclusion step.