resolves #4 add transform-group option to use single wrapper element

[mojavelinux]

• using single wrapper to scale slides if option is transform-group
• fix tests
• add tests for transform-group option

[mojavelinux]

As a side note, tests don't work on Firefox for some reason. However, I did manually testing in Firefox and it works great.

[mojavelinux]

I realized that when transform-group is specified, it still uses zoom in Chrome. This differs from the transform option, which uses transform for all browsers. So we have an extra degree of configuration here. Should we switch to an options map so that we can have a separate flag for whether to wrap each slide or the group of slides?

zoom with transform (on group) fallback

{ applyTo: 'group' }

transform (on group)

{ method: 'transform', applyTo: 'group' }

The default would be:

{ applyTo: 'slide' }

[mojavelinux]

When applyTo is "group", I'd also move the zoom to this wrapper element so that the change is consistent.

[mojavelinux]

Or maybe we can simplify the option name to "on":

{ method: 'transform', on: 'group' }

Is there a value you prefer to describe the group of slides instead of "group"?

[mojavelinux]

Another possibility is to use a fallback chain, like:

scale('zoom|transform group')

vs

scale('zoom|transform slide')