add support to selectively disable array draggable by form configuration

[sdetweil]

fixes #336

[tchapi]

Hi @sdetweil

Can you fix the rogue spaces that this PR adds (line 261 for instance, etc — see https://github.com/jsonform/jsonform/pull/348/files), and also provide an example schema so I can test this ?

Thanks a lot for your work !

[tchapi]

EDIT: I corrected the spaces — you can merge master into your branch again — or rebase (same for your other PRs)

[sdetweil]

attached file for playground

two cases, with drag enabled.

1. if u have a field with an ace editor in an array, and click in it, you are stuck in drag mode
   only way out is to right click, then exit the right click. shouldn't happen

2. if drag is enabled, tabs in tabarray are draggable, but in my app that operation doesn't mean anything, so its should be tuned off, but drag is enable form wide. need something selective... drag is set to false in the form attached (selectively)

schema.json.txt