Change from LESS to SASS (#71)

[xipasduarte]

Resolving issue #71.
Added bootstrap-sass to bower.json and removed bootstrap.
Added gulp-sass to package.json and removed gulp-less.

Notes:

• Work needs to be done in order to handle some of the @extend commands used to "import" styles from Bootstrap's classes into other elements. (The use of placeholders/mixins should be considered.)
• There seems to be an issue with the Gulp task build:styles that I was unable to solve:

Job 2, 'gulp build:styles' terminated by signal SIGBUS (Misaligned address error)

[goblindegook]

Let's give 3.3.4 a try. Should cause no major (or minor) headaches.

[goblindegook]

+1 for Sass placeholders, I created issue #74 to address it.

I'll look into your build issue soon, otherwise everything looks good to go.