Add extra config. options to sass-build

[Chris-V]

We need to apply extra transformations to our sass build. ionic-gulp-sass-build doesn't allow us to pipe such transformations. In order to keep ionic's default values and pipe additional transformations I suggest a hook function is added to the options object.

Here, I added the following properties:

• srcOptions: because we need to set the {base: 'abc/abc'} options for gulp.src

• hookFunction: it enables us to set our extra transformations. ie:

  options = {
   hookFunction: function(stream) {
     return stream.pipe(mySuperTransformation());
   }
  }