[igx-select] Footer element

[sboykova]

Is your feature request related to a problem? Please describe.

I need an element which is always into view when scrolling the select items

Describe the solution you'd like

I want to have a way to define igx-select footer element.

Additional context

[StefanIvanov]

Have you considered using the igx-combo as it support header and footer templates?

[sboykova]

igx-combo comes with multiple selection - and we just need the single selection igx-select.

[StefanIvanov]

OK we have discussed with @radomirchev to add the same type of templatable header and footer areas to the igx-select as we have in the combo.
I have added a story at the bottom of dev stories in the spec