Bringing appearance and behaviour closer to standard widget like
DropdownWidget:
- Amending color to be (closest) aligned to WikimediaUI color
palette, but switch normal and `:hover`/`:focus` state in order not
to be too disruptive of a change and align with rest of Vector tabs,
- removing obsolete JS functionality as IE 6 as only major browser
affected does receive the menu items as tabs nonetheless and replacing
with simple CSS selector,
- removing unnecessary and obsolete images and
- Lessifying selector
Bug: T153043
Change-Id: Ia15480162bb8f923d0e9b6e42ca90c2c880978de
