MediaWiki theme: Make CapsuleItemWidget behave similar to other widgets
MediaWiki theme: Make CapsuleItemWidget behave similar to other widgets

Changing CapsuleItemWidget to align behaviour with other
widgets, like ButtonWidget by
 - align to WikimediaUI color palette,
 - adding transitions,
 - adding `:hover` state
 - putting CSS/Less code in same order as other widgets and
 - moving code bits that are for certain state (`disabled`/`enabled`)
   only to those selectors.

Change-Id: I04f5b82dde1cec32489c8c156daeb575236b27fe

wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui