Fix usage of useref, wiredep with bower_components

This PR fix https://github.com/Swiip/generator-gulp-angular/issues/94 and https://github.com/Swiip/generator-gulp-angular/issues/93

@mburbea @Scottmey @jbaroudi  can you testing this version before merge.

https://github.com/yeoman/generator/wiki/Testing-generators

Follow this wiki page to test in local env with https://github.com/eleven-labs/generator-gulp-angular branch fix