Previously all categories were displayed as search engine tabs.
This commit changes that so that only the categories listed under
categories_as_tabs in settings.yml are displayed.
This lets us introduce more categories without cluttering up the UI.
Categories not displayed as tabs can still be searched with !bangs.
* rework selection UI in pref (fix based on: 78643e9f43)
* moved search filters underneath categories
* cut params from url and replace / with ›
* make h3 and url in article bigger
* add safe search select to search filter (this will not override settings and only be valid while on result page in a session)
* make search form button not overlap each other when js is disabled
* 1rem padding around preview image and thumbnail in default article template
* update from ionicons-npm to ionicons ver.5
* drop the webfont built by grunt for icons
* built icons.html template for inlining icons with jinja2 into html
* update icon to use mostly the outline version
* add icons to categories and do not display them on mobile to save space
* remove all legacy ion icon font files from simple theme
* icons.html is added in this commit since make statc.build.restore requires git to know the file already
* cleanup error-dialog
* rework search form as grid layout
* remove various paddings and margins
* add logo and link to index to search form
* make categories bigger on phone
