Added tabs to search page

Tabs have been added to the search page to allow toggling between facet and spatial filters. This replaces the accordion toggling that was previously implemented.

The Bootstrap tab component has been used and some styling applied. Two css variables have been added: --filter-tab-border-colour that simplifies changing the search tab border colour (fiddlier than you might think); and --search-map-header-height to help fit the leaflet map to the remaining available height after any changes to the search header. Custom styling has been added to style-eidc.less and style-ukeof.less, other catalogues just get generic settings.

Closes EMC-126