ui: table - add support for translated column headers

[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/stark/blob/master/CONTRIBUTING.md#got-a-question-or-problem

Current behavior

If a translation key is used for the column headers (instead of an actual label), the headers are not translated.

Expected behavior

The column headers should be correctly translated.

Minimal reproduction of the problem with instructions

1. Add a Stark Table component to your template.
2. In the StarkTableColumnProperties object to define the columns, specify a translation key as the column's label.
3. The column headers are not translated, the translation key is displayed 'as is'.

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

A Table component with a seamless integration with translations.

Environment

Angular version: 7.1.0
Stark version: 10.0.0-beta.1

[christophercr]

Closed in #959