style.css: add fontawesome to beginning of font list

If there is some other font installed that 1) matches the four existing
font families and 2) provides its own glyph in the private use area used
by Awesome, then that font's glyph will be used instead of the intended
icon.

For example, the following character (U+F001, "music"): 
...looks like a pair of musical notes in fontawesome, but DejaVu Sans
also provides a glyph, which looks like a couple of squares. DejaVu Sans
matches first when "sans-serif" is requested, so its (unrelated) glyph
is used.

resources/style.css

@@ -1,6 +1,6 @@
 * {
     /* `otf-font-awesome` is required to be installed for icons */
-    font-family: Roboto, Helvetica, Arial, sans-serif;
+    font-family: FontAwesome, Roboto, Helvetica, Arial, sans-serif;
     font-size: 13px;
 }