Add Offsets, Generate Grids by Sass function

I've added Offsets to the grid system so we don't have
to fill up our websites with empty divs that contain spans
for spacing.

Spans and Offsets are generated using SASS functions to
cut down on the amount of code in the SASS Files and make it
more readable for developers.

We lose the ability to use @extend but that is not as important
as we minimize the css anyways.
Add offsets, move related grid funcs to sep file.

I added offsets to the grid system to bring our system in line
with other modern grid systems like bootstrap.js, blueprint.css,
960grid.css, etc. This also has the added benefit of preventing
webdevs from having to clutter up their html with empty divs to
handle positioning.

I decided to go with a single offset method as opposed to a push
and pull system as I personally think it is a much simpler way to
implement an offset system.

I moved the common grid functions and mixins to include/_grid_mixins.scss
to make it easier to implement future grids for different screen sizes.

-Calvin Rodo
calvin.rodo@hrsdc-rhdcc.gc.ca
remove unnecessary whitespace
Adding license header to file
Merge pull request #1105 from CalvinRodo/grid-offset

Add offset and clean up Sass code in grid functionality.