Make timestamp text selectable

Previously we only declared the message body as selectable, but Chrome's
implementation of user-select is a little quirky in that it allows
unselectable text to be copied if you select elements around it. Oddly
enough, styling the entire bubble contents as selectable, including the
timestamp, actually prevents chrome from copying the timestamp text when
it's not supposed to, i.e., when triple-clicking the message body.

Fixes #887

// FREEBIE

stylesheets/_conversation.scss

@@ -289,13 +289,13 @@ li.entry .error-icon-container {
     margin-left: 8px;
     max-width: 30em;
     text-align: -webkit-auto;
+    -webkit-user-select: text;
 
     @media(max-width: $big-avatar-min-width - 1px) {
       max-width: calc(100% - 45px - #{$error-icon-size}); // avatar size + padding + error-icon size
     }
 
     .body {
-      -webkit-user-select: text;
       white-space: pre-wrap;
 
       a {
@@ -387,7 +387,6 @@ li.entry .error-icon-container {
     .bubble {
       .content {
         font-style: italic;
-        -webkit-user-select: text;
       }
 
       &::before, &::after {

stylesheets/manifest.css

@@ -1122,14 +1122,14 @@ li.entry .error-icon-container {
     word-wrap: break-word;
     margin-left: 8px;
     max-width: 30em;
-    text-align: -webkit-auto; }
+    text-align: -webkit-auto;
+    -webkit-user-select: text; }
     @media (max-width: 899px) {
       .message-container .bubble,
       .message-list .bubble {
         max-width: calc(100% - 45px - 24px); } }
     .message-container .bubble .body,
     .message-list .bubble .body {
-      -webkit-user-select: text;
       white-space: pre-wrap; }
       .message-container .bubble .body a,
       .message-list .bubble .body a {
@@ -1209,8 +1209,7 @@ li.entry .error-icon-container {
     clear: left; }
   .message-container .control .bubble .content,
   .message-list .control .bubble .content {
-    font-style: italic;
-    -webkit-user-select: text; }
+    font-style: italic; }
   .message-container .control .bubble::before, .message-container .control .bubble::after,
   .message-list .control .bubble::before,
   .message-list .control .bubble::after {