Search for users in autocomplete popup + other tweaks

- Highlight matching parts of usernames
- Fix positioning edge cases

extensions/mentions/less/mentions.less

@@ -30,13 +30,25 @@
   max-height: 200px;
   overflow: auto;
   position: absolute;
+
+  & mark {
+    padding: 0;
+  }
+  & > li > a:hover {
+    background: none;
+  }
 }
 .post-preview {
   color: @fl-body-muted-color !important;
 
   & .avatar {
-    .avatar-size(32px);
-    margin: 3px 0 3px -45px;
+    .avatar-size(24px);
+    margin: 0 0 0 -37px;
+
+    .suggestion-post& {
+      margin-top: 3px;
+      margin-bottom: 3px;
+    }
   }
   & .username {
     color: @fl-body-color;
@@ -44,7 +56,7 @@
   }
 }
 .post-preview-content {
-  padding-left: 45px;
+  padding-left: 37px;
   overflow: hidden;
   line-height: 1.7em;
 }