Make non-message components of UI non-selectable (#3078)

* Make sidebar non-selectable
* Prevent selection of avatar and context menu text in conversation view
* Make loading view and conversation placeholder view non-selectable
* Make settings view contents non-selectable

stylesheets/_global.scss

@@ -457,6 +457,7 @@ $loading-height: 16px;
   background-color: white;
   display: flex;
   align-items: center;
+  user-select: none;
 
   .content {
     margin-left: auto;

stylesheets/_index.scss

@@ -31,6 +31,7 @@
 
   float: left;
   width: 300px;
+  user-select: none;
 
   .content {
     overflow-y: scroll;
@@ -243,6 +244,8 @@ input.search {
 
 .conversation.placeholder {
   text-align: center;
+  user-select: none;
+
   .container {
     position: absolute;
     height: 100%;

stylesheets/_modules.scss

@@ -1275,6 +1275,7 @@
 
 .module-conversation-header__avatar {
   min-width: 28px;
+  user-select: none;
 }
 
 .module-conversation-header__title {
@@ -2554,6 +2555,7 @@
   padding-bottom: 8px;
   border: 1px solid $color-dark-05;
   opacity: 0;
+  user-select: none;
 }
 
 .react-contextmenu--visible {

stylesheets/_settings.scss

@@ -1,4 +1,6 @@
 .settings {
+  user-select: none;
+
   &.modal {
     padding: 0;
     background-color: transparent;