Extract app theme scss to external files (#524)

frontend/assets/scss/theme/variables.scss

@@ -0,0 +1,22 @@
+// Primary color
+$primary: #34B891;
+$primary-invert: findColorInvert($primary);
+
+$colors: (
+		"primary": ($primary, $primary-invert),
+		"info": ($info, $info-invert),
+		"success": ($success, $success-invert),
+		"warning": ($warning, $warning-invert),
+		"danger": ($danger, $danger-invert),
+);
+
+// Links
+$link: $primary;
+$link-invert: $primary-invert;
+$link-focus-border: $primary;
+
+// Disable the widescreen breakpoint
+$widescreen-enabled: false;
+
+// Disable the fullhd breakpoint
+$fullhd-enabled: false;