Add CSS selectors to left- or rightalign slides

lectures/custom.scss

@@ -22,6 +22,14 @@ h2 {
     text-align: center;
 }
 
+.reveal .leftalign {
+    text-align: left;
+}
+
+.reveal .rightalign {
+    text-align: right;
+}
+
 .reveal code:not(.sourceCode) {
     /*-- reduce size of inline code --*/
     font-size: smaller;