Enhance Development Environment

**-- Please review and discuss before merging --**

Main changes were

* *gulp* instead of make for `livereload` and concurrent tasks
* cleaner folder structure with mainly `src` and `dist` plus `node_modules`
* cleanup last reminders of wordpress plugin

The new folder structure in detail:

    src // all source files and libraries except node modules
     |- libs // external dependencies to include
     |- example // example files
     |- sass // SCSS project files
     |- js // application code
     |- img // source images

    dist // will be built entirely from sources
     |- js // production code with vendor libraries included
     |- example // this will be served locally
     |- css // processed stylesheets
     |- font // icon and possibly other fonts packaged with the app
     |- bin // flash and silverlight fallbacks and other binaries