Added textAlpha and textActiveAlpha to Button and ButtonGroup.

doc/out/ThemeRed.html

@@ -1472,7 +1472,7 @@ The primaryColor is set to 0xd92f31.</p></div>
     
         
         <div class="tag-source">
-            <a href="pixi_theme.js.html#line260">theme.js:260</a>
+            <a href="pixi_theme.js.html#line264">theme.js:264</a>
         </div>
         
     </div>
@@ -1598,7 +1598,7 @@ const app = new PIXIApp({
 
         <footer class="content-size">
             <div class="footer">
-                Documentation generated by <a target="_blank" href="https://github.com/jsdoc3/jsdoc">JSDoc 3.6.3</a> on Fri Oct 11 2019 09:19:28 GMT+0200 (Mitteleuropäische Sommerzeit)
+                Documentation generated by <a target="_blank" href="https://github.com/jsdoc3/jsdoc">JSDoc 3.6.3</a> on Tue Oct 15 2019 14:56:00 GMT+0200 (Mitteleuropäische Sommerzeit)
             </div>
         </footer>
     </div>