demo: improve examples and styling

[christophercr]

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/ngx-form-errors/blob/master/CONTRIBUTING.md#got-a-question-or-problem

Current behavior

The Demo app is very basic and without styling.

Expected behavior

The Demo should have a very nice look and feel and show all the features provided by the library.

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

Fully working Demo app that catches the attention of the developer focusing on the added value of the library.

Environment

NgxFormErrors version: 1.0.0-alpha

[christophercr]

@cnomes I have improved the demo app of this library. Unfortunately I've spent a lot of time in doing it because of some weird Angular issues until I've managed to fix them. So... could I ask you a favor? Could you help me to improve the styling so that it looks nice for the demo of today? In fact, the 3 pages in the demo have exactly the same CSS so I hope the styling is easy to fix 😉

The demo is in this branch: feature/demo-improvements
Thanks a lot!

[carlo-nomes]

@christophercr, sure thing. I'll have a look at it. 👍