Refine template layout with flex

Add usage of angular flex classes and properties
Use fxFlex to fill all available screen space
Remove old scss properties which are no longer used

src/app/app.component.html

-<div class="app-fullscreen">
+<div fxLayout="column" fxFill>
   <mat-toolbar color="primary">
     <mat-toolbar-row>
       <span class="app-toolbar-title">
@@ -7,7 +7,7 @@
       <!-- Insert navigation module here -->
     </mat-toolbar-row>
   </mat-toolbar>
-  <div fxLayout="row" fxLayoutAlign="start start" fxLayoutGap="20px" class="app-main">
+  <div fxFlex>
     <router-outlet></router-outlet>
   </div>
 </div>

src/app/app.component.scss

 @import '../theme/_variables.scss';
-
-.app-fullscreen {
-  width: 100%;
-  height: 100%;
-  > div {
-    padding: 10px;
-  }
-}
-
-.app-main {
-  /* Insert more styles here */
-}