[Frontend] CSS for better startup

Fixes #1966
- Transitions and opacity styles moved to new _app-start.scss,
which loads at the very end of all other CSS needed by the app;

platform/commonUI/general/res/sass/_app-start.scss

@@ -0,0 +1,11 @@
+// At the last, hide .l-splash-holder and show .holder-all
+.l-splash-holder.fadeout {
+    @include trans-prop-nice($props: opacity, $dur: 1000ms);
+    opacity: 0;
+    pointer-events: none;
+}
+
+.user-environ .holder-all {
+    opacity: 1;
+    pointer-events: inherit;
+}

platform/commonUI/general/res/sass/_main.scss

@@ -76,9 +76,11 @@
 @import "items/item";
 @import "mobile/item";
 
-
 /********************************* TO BE MOVED */
 @import "autoflow";
 @import "features/imagery";
 @import "features/time-display";
 @import "widgets";
+
+/********************************* APP STARTUP */
+@import "app-start";

platform/commonUI/general/res/sass/startup-base.scss

@@ -32,11 +32,7 @@ body, html {
 }
 
 .l-splash-holder {
-    // Main outer holder.
-    @include transition-property(opacity);
-    @include transition-duration(500ms);
-    @include transition-timing-function(ease-in-out);
-    @include transition-delay(1s);
+    // Main outer holder for splash.
     position: absolute;
     top: 0;
     right: 0;
@@ -44,16 +40,18 @@ body, html {
     left: 0;
     z-index: 10000;
     opacity: 1;
-    &.fadeout {
-        opacity: 0;
-        pointer-events: none;
-    }
     .l-splash {
         // The splash element.
         @include splashElem();
     }
 }
 
+.user-environ .holder-all {
+    // Gets shown again by main CSS, once loaded
+    opacity: 0;
+    pointer-events: none;
+}
+
 @media only screen and (max-device-width: 767px) {
     .l-splash-holder .l-splash {
         @include splashElem(0);