Some gulp file refactoring. Read:

1) paths.compile  'client/**/*.js' was to vague. Actually it involves
client/app/build. So suggested pattern is:
client/**/js/**/*.js'
2) Harmony for JSX compiler is enabled by default. ES6 transpiling is a
good thing.
3) Unit tests don’t start if test file doesn’t exists.
4) Added task transpile.