Add languages option feature

[maxwellpeterson-wf]

As we discussed here: https://github.com/Workiva/wGulp/pull/63#discussion_r19161225

Creating the PR into the depTree branch so this portion of the code can be reviewed and discussed separately.

This allows us to specify a languages option in a wGulp project like so:

var customizedOptions = {
    languages: ['javascript', 'typescript']
};

The defaults are to include all supported languages:

    languages: ['javascript', 'typescript', 'coffeescript', 'livescript']

As languages are removed from this list, wGulp will automatically trim the tasks it runs for builds.

@trentgrover-wf @evanweible-wf @shanesizer-wf @theisensanders-wf

[trentgrover-wf]

1 small comment, otherwise +1

[trentgrover-wf]

+1

[evanweible-wf]

+1

[shanesizer-wf]

Very cool @maxwellpeterson-wf