Added the dieHolder array -- cleaned up HTML and CSS

# Changes #

## test.js ##
- pushed the **dice** object onto the **dieHolder** array.
- fixed **roll** function in Roll Button test - just changed *roll* to *roll()*.

## main.scss ##
- removed all the default CSS so it's ready for our own stuff.

## app/index.html ##
- removed all the default HTML so it's ready for our own stuff.

## main.js ##
- added the **dieHolder** array.