Suggestion: add more short keys

Hi! :)

I love your code but I would like to suggest adding more shortkeys like the [shift] button. I think it could really be handy to have it in the default option for everyone; even though it is easily added. ;) Have pasted an example below. Anyways, really awesome code and appriciate this plugin a lot!!

Yours Sincerely,

LonelySquid

_scroll-through-time.js_
`enum: [
{
value: "none",
description: "No modifier key used"
},
{
value: "altKey",
description: "Alt (Option) key"
},
{
value: "ctrlKey",
description: "Control key"
},
{
value: "shiftKey",
description: "Shift key"
}
]`

Start in _scroll-through-time.js_ and inspect the existing short-key enum shown in the issue. Determine which additional modifier options should be included by default, then verify that the configuration exposes them consistently with the existing entries.

Written by the indexing model from the issue text.