use css truncate everywhere and remove StringUtils.truncate function (#513)

Co-authored-by: robs <git@robs.social>

lib/pinchflat_web/controllers/sources/source_html/edit.html.heex

@@ -2,7 +2,7 @@
   <.link href={~p"/sources"}>
     <.icon name="hero-arrow-left" class="w-10 h-10 hover:dark:text-white" />
   </.link>
-  <h2 class="text-title-md2 font-bold text-black dark:text-white ml-4">
+  <h2 class="text-title-md2 font-bold text-black dark:text-white ml-4 truncate">
     Editing "{@source.custom_name}"
   </h2>
 </div>