Refactor build tasks

Decouple static "main" keys in mconfig.json and refactor tasks to support many output files.

Added:
- scripts.js: Array of output files (such as 'app.js') to iterate over to bundle JS files.
- styles.js: Array of input files (such as 'main.css' and 'critical.css') to iterate over to compile Sass files.
- svgs.js: Array of output files (such as 'sprite.svg') to iterate over to compile SVG spritesheets.

Changed:
- mconfig.json: Decouple entry points to individual tasks to allow for more flexibility in projects.
- concat.js: Refactor function to use promises to build list of JS files to concatenate.
- message.js: Replace if statements with switch for improved readability.
- message.js: If timerID provided with "waiting" type, log time.
- watch.js: Change CSS and JS reload watch paths to include all files.
- Sorted imports by path.

build/build.js

@@ -1,9 +1,9 @@
-import { buildScripts } from './scripts.js';
 import { concatVendors } from './concat.js';
+import { compileScripts } from './scripts.js';
 import { compileStyles } from './styles.js' ;
-import { generateSpriteSVG } from './svgs.js' ;
+import { compileSVGs } from './svgs.js' ;
 
-buildScripts();
 concatVendors();
+compileScripts();
 compileStyles();
-generateSpriteSVG();
+compileSVGs();