Make links list scrollable in header

[rohitpaulk]

All elements except the list of links (Catalog, contests, badges etc. etc.) should not shrink - if there isn't space, the links list should become scrollable.

[VasylMarchuk]

Question about this, would you like just a regular browser scroll, or some kind of visual < and > buttons on the sides that can be pressed to scroll as well? @rohitpaulk

[rohitpaulk]

Question about this, would you like just a regular browser scroll, or some kind of visual < and > buttons on the sides that can be pressed to scroll as well? @rohitpaulk

@VasylMarchuk just regular browser scroll is fine! We don't expect this to happen too much (there's a pretty narrow screen size range where it will), just don't want it to look completely broken