[WIP] Add Pannable plugin

[owen-m1]

This PR implements or fixes...

Adds a Pannable plugin to Draggable, for panning around elements that have overflow in their parent container. Effectively making it a replacement for scrollbars.

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This PR closes the following issues...

#309 …

Does this PR require the Docs to be updated?

Yes …

Does this PR require new tests?

Yes …

This branch been tested on... (click all that apply / add new items)

Browsers:

• [ ] Chrome version
• [ ] Firefox version
• [ ] Safari version
• [ ] IE / Edge version
• [ ] iOS Browser version
• [ ] Android Browser version

[itsmunim]

Hi @owen-m1,

I had a general suggestion. Seems like one commit is containing too much of a code changes. Could it be broken down into smaller frequent commits, so that the history is much easier to follow and review by commits?

Thanks.

[owen-m1]

@dibosh I completely agree with you but I was following the PR guide which said to force-push to one commit. I don't like this either D: