fix(styles): use pointer cursor for 'a' element by default

Fixes LIIP-128.
refactor(styles): reduce repetition by using scss nesting in nav-tabs
style(nav-tabs): show cursor pointer also for active tab

Bootstrap overrides the default behavior for active tab, we need to set cursor type explicitly.
Merge pull request #88 from HSLdevcom/liip-128

Liip 128