Slightly widen index sidebar, overflow buttons properly

First half of #349 fix. Supersedes #734 (190px wide instead of 200px, correctly modify margin-left of .sideNavOffset, more descriptive commit message)

less/forum/IndexPage.less

@@ -6,8 +6,7 @@
     margin-bottom: 20px;
 
     .Button {
-      display: block;
-      width: 100%;
+      .Button--block();
     }
   }
 }

less/lib/Button.less

@@ -192,6 +192,8 @@
 .Button--block {
   display: block;
   width: 100%;
+  overflow: hidden;
+  text-overflow: ellipsis;
 
   // Vertically space out multiple block buttons
   + .Button--block {

less/lib/sideNav.less

@@ -95,7 +95,7 @@
     float: left;
 
     &, > ul {
-      width: 175px;
+      width: 190px;
     }
     > ul {
       margin-top: 30px;
@@ -119,6 +119,6 @@
 @media @desktop-up {
   .sideNavOffset {
     margin-top: 30px;
-    margin-left: 225px;
+    margin-left: 240px;
   }
 }