fix(stark-ui): update some component styling to fix bugs

[carlo-nomes]

• fix footer overflow
• fix footer hovering above bottom of screen
• removed unused redundant DOM from app.component.html (showcase / starter)

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/NationalBankBelgium/stark/blob/master/CONTRIBUTING.md#-commit-message-guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: #1169

What is the new behavior?

Footer sticks to bottom.

Does this PR introduce a breaking change?

[x] Yes
[ ] No

• stark-app-sidenav-content should not be applied to a wrapper element (div) anymore. Replace it with a ng-container.
  This ensures the footer is always at the bottom. (see Starter for an example)

[coveralls]

Coverage remained the same at 93.445% when pulling 764ee3b on cnomes:fix/viewport-issues into 50e9bbe on NationalBankBelgium:master.

[coveralls]

Coverage increased (+0.005%) to 93.451% when pulling 01257d9 on cnomes:fix/viewport-issues into 5a9df97 on NationalBankBelgium:master.

[christophercr]

LGTM... except for the fact that on IE the pages are empty now :p

[carlo-nomes]

@christophercr I updated the PR. I also needed to change some CSS of the table-of-contents component

[christophercr]

Now although the issue on IE is solved, as I showed you there are 2 issues:

1. The Table of Contents doesn't react anymore to the scrolling event to activate the topic in which you are.
   Before:
   
   Now:
   

2. The scrollbar of the page (Getting Started) is not always clickable... apparently the Table of Contents overlaps in front of it.

[carlo-nomes]

@christophercr I updated the PR and added #1172 😄

[christophercr]

Now Travis is failing because of this error on the unit tests of the Showcase:

src/app/shared/components/table-of-contents/table-of-contents.component.spec.ts(42,13): error TS2339: Property 'scrollToAnchor' does not exist on type 'TableOfContentsComponent'.

[carlo-nomes]

@christophercr I updated the PR 😄

[christophercr]

LGTM

As discussed, the regression caused in the Table of Contents will be tackled in #1172 which has a lower priority that the issue solved in this PR ;)