Gh154 restructure less build to allow ampersand to not have fuelux in parents

[chriscorwin]

This change is to achieve parity with fuelux, and is essentially identical to: ExactTarget/fuelux#1047

Purpose

The proposed change would allow us to begin to use the & parent selector that LESS provides more effectively.

Overview

The less build should be able to be slightly restructured so that the .fuelux wrapper class name is not in the parent-chain (&) during the main LESS compilation, and instead gets tacked onto the front of the rules after the fact.

The CSS file ultimately output ought not be any different after making this change, since the & selector currently goes under-utilized (due, of course, to the quirks of our current process).

Simple example

From the LESS documentation on Changing Selector Order.

Given the following code:

.header {
  .menu {
    border-radius: 5px;
    .no-borderradius & {
      background-image: url('images/button-background.png');
    }
  }
}

...the way we are currently building the LESS would render the .css as:

.fuelux .header .menu {
  border-radius: 5px;
}
.no-borderradius .fuelux .header .menu {
  background-image: url('images/button-background.png');
}

Note the stray .fuelux that is inserted after the .no-borderradius selector, which is not what the developer intended.

The restructure would output as:

.fuelux .header .menu {
  border-radius: 5px;
}
.fuelux .no-borderradius .header .menu {
  background-image: url('images/button-background.png');
}

The Actual Restructure Proposal

Introduces a new .less file at less/fuelux-override.less that does the initial compilation of the fuelux overrides not inside the .fuelux wrapper.

It outputs a temporary "non-namespaced" file, located at less/fuelux-override-no-namespace.less.

The fuelux-mctheme.less is changed so that it imports the less/fuelux-override-no-namespace.less file inside the wrapper -- tacking the .fuelux "namespace" onto the rules for the overrides.

// Fuel UX override
.fuelux {
    @import "fuelux-override-no-namespace.less";
}

The grunt task doing this outputs the resulting .css into it's final home at /dist/css/fuelux-mctheme.css, and then deletes the temporary file.

The temporary file is also added to .gitignore to ensure that a failed LESS build does not result in the temp file not being deleted and inadvertently checked into the repository.