core: integrate angular-in-memory-web-api from showcase in stark-core

[SuperITMan]

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[ ] Bug report  
[X] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/NationalBankBelgium/stark/blob/master/CONTRIBUTING.md#got-a-question-or-problem

Current behavior

In the showcase, we replaced json-server by angular-in-memory-web-api and it works well.
However, this module is only available in showcase.

Expected behavior

Provide our configuration for angular-in-memory-web-api in Stark-Core, in addition to our support for json-server in Stark-Build.

What is the motivation / use case for changing the behavior?

Improvement.