Add a vendor.cssPreprocessor in all cases

[Swiip]

As said in #439, we should organize a vendor.cssPreprocessor regardless of the ui framework chosen. It's not because the main ui framework has not a version for your css preprocessor that you'll never have a dependencies which has one.

I also discovered that we injected css preproc deps in the index.cssPreprocessor and not in the vendor so I moved it which create a reason of existence for vendor.cssPreprocessor even when it's empty.

Finally I took the change for creating a sub folder structure in the src/app folder which was a mess.

fix #439

[zckrs]

// injector
// endinjector

should be stay in index.cssPrepro to manage the application's styles in a single file after a build.

For vendor.cssPrepro may be use Wiredep to inject all vendor's styles in a single file

[Swiip]

Should be better know.

• index.cssPrepro is injected with the source files (which still has to be illustrated with a navbar.cssPrepro.
• vendor.cssPrepro is injected with the bower deps though wiredep. It still depends of the quality of the bower.json of the deps, for example foundation doesn't link the scss version.

[zckrs]

👍 nice