feat(flag): use emoji svg flags with (auto) sizing

This PR replaces the sprite flag backgrounds by the new emoji flags keeping existing code bases backward compatible (you still use <i class="uk flag"></i> as before)

Additionally

almost all countries are available now (famfamfam sprite misses a lot of flags)
flags can now be sized
they are autosized by current font-size if no size class is given
the old sprite approach was kept into an additional theme famfamfam which one can easily switch back by changing the flag theme in theme.config

src/definitions/elements/flag.less

@@ -24,29 +24,19 @@
 *******************************/
 
 i.flag:not(.icon) {
-  display: inline-block;
-
-  width: @width;
-  height: @height;
-
-  line-height: @height;
-  vertical-align: @verticalAlign;
-  margin: 0 @margin 0 0;
-
-  text-decoration: inherit;
-
   speak: none;
-  -webkit-font-smoothing: antialiased;
   backface-visibility: hidden;
 }
 
-/* Sprite */
 i.flag:not(.icon):before {
+  content: '\00A0\00A0\00A0\00A0\00A0\00A0\00A0';
   display: inline-block;
-  content: '';
-  background: url(@spritePath) no-repeat -108px -1976px;
-  width: @width;
-  height: @height;
+  line-height: @flagLineHeight;
+  background-repeat: no-repeat;
+  background-position: center center;
+  & when not (@flagFileType = 'svg') {
+    background-size: contain;
+  }
 }
 
 .loadUIOverrides();