feat(nb-rangepicker): range showing before selection

[jedi-night]

Issue type

I'm submitting a ... (check one with "x")

• [ ] bug report
• [x] feature request

Issue description

Current behavior:

The range selection is visible only if I select the 2 dates.

Expected behavior:

It will be awesome if we can see the range selection before it selected with a lighter color between my first date and the "hover" date :)