add babel core, gulp-babel, autoprefixer, and gulp-postcss to gulp process, add gulp babel so that ES6 can be used, convert gulp-autoprefixer to autoprefixer in conjunction with gulp-postcss, add .browserlistsrc based on suggestions from autoprefixer/postcss/browserlists docs.

Author: kelsS

.browserslistrc

@@ -0,0 +1,10 @@
+# please see https://github.com/browserslist/browserslist for more info
+# These settings can be changed depending on what browsers your project is supporting
+
+>= 0.01%
+Last 5 versions
+last 8 iOS versions
+Firefox >= 28
+IE 10 # sorry
+IE 11 # sorry
+dead # sorry