Improved sidebar, Added misc rules and options

Update index.php, sidebar.php, and 6 more files...

scss/core/sizing.scss

@@ -21,12 +21,20 @@
 .w-half {
 	width: 50%;
 }
+.wm-half {
+	max-width: 50%;
+}
 
 .h-half {
 	height: 50%;
 }
+.hm-half {
+	max-height: 50%;
+}
 
-// Pixels Sizing (Deprecated, disabled by default, use custom rules !)
+// Pixels Sizing
+// These rules are deprecated and disabled by default.
+// You should preferably use custom site-specific or app-specific rules instead !
 @if($add-px-sizing-rules) {
 	// 50, 100, ..., 250 px
 	@for $_ from 1 through 5 {

scss/core/text.scss

@@ -166,3 +166,7 @@ s, .t-strikethrough {
 	// Should be 35% TBH
 	opacity: 45%;
 }
+
+.t-noselect {
+	user-select: none;
+}