Remove tff fonts & Temporarily show system font while loading fonts

tff fonts IMO can be removed since woff and woff2 are supported by all modern browsers (in fact, woff support was added to Firefox in 2010).

Temporarily show system font while loading fonts (even though we talk about icons here). Recommendation from Chrome Lighthouse audit, see https://developer.chrome.com/docs/lighthouse/performance/font-display/?utm_source=lighthouse&utm_medium=devtools#how-to-avoid-showing-invisible-text.

Signed-off-by: Florian Hotze <[email protected]>

bundles/org.openhab.ui/web/src/css/icons.css

@@ -6,8 +6,8 @@
   src: local('Material Icons'),
        local('MaterialIcons-Regular'),
        url(../fonts/MaterialIcons-Regular.woff2) format('woff2'),
-       url(../fonts/MaterialIcons-Regular.woff) format('woff'),
-       url(../fonts/MaterialIcons-Regular.ttf) format('truetype');
+       url(../fonts/MaterialIcons-Regular.woff) format('woff');
+  font-display: swap;
 }
 .material-icons {
   font-family: 'Material Icons';
@@ -32,9 +32,9 @@
   font-family: 'Framework7 Icons';
   font-style: normal;
   font-weight: 400;
-  src: url("../fonts/Framework7Icons-Regular.woff2") format("woff2"),
-       url("../fonts/Framework7Icons-Regular.woff") format("woff"),
-       url("../fonts/Framework7Icons-Regular.ttf") format("truetype");
+  src: url(../fonts/Framework7Icons-Regular.woff2) format('woff2'),
+       url(../fonts/Framework7Icons-Regular.woff) format('woff');
+  font-display: swap;
 }
 .f7-icons {
   font-family: 'Framework7 Icons';