Add webkit-prefixed user-select attributes (#41)

It turns out that WebKit uses its own prefix for user-select so I'm adding this everywhere we currently define user-select, as well as a few new places

frontend/app/block/block.less

@@ -31,13 +31,12 @@
     justify-content: center;
     background-color: var(--panel-bg-color);
     user-select: none;
+    -webkit-user-select: none;
     cursor: default;
 
     .block-header-text {
         padding: 0 5px;
         flex-grow: 1;
-        user-select: none;
-        cursor: default;
     }
 
     .close-button {

frontend/app/view/directorypreview.less

@@ -20,6 +20,7 @@
                     height: 100%;
                     cursor: col-resize;
                     user-select: none;
+                    -webkit-user-select: none;
                     touch-action: none;
                     width: 2px;
                     background: linear-gradient(var(--border-color), var(--border-color)) no-repeat center/2px 100%;

frontend/app/workspace/workspace.less

@@ -46,8 +46,6 @@
     height: 32px;
     border-bottom: 1px solid var(--border-color);
     flex-shrink: 0;
-    user-select: none;
-    cursor: default;
 
     .tab {
         display: flex;
@@ -57,6 +55,8 @@
         height: 100%;
         font-weight: bold;
         border-right: 1px solid var(--border-color);
+        user-select: none;
+        -webkit-user-select: none;
         cursor: pointer;
         position: relative;
 

frontend/faraday/lib/tilelayout.less

@@ -51,6 +51,8 @@
             position: absolute;
             top: 10000px;
             white-space: nowrap !important;
+            user-select: none;
+            -webkit-user-select: none;
         }
     }