Add back dragbox functionnality

[gberaudo]

Due to a change in Cesium, the functionnality had to be removed in #313. See PR commits for detail.

The functionality was described in #13.

Feel free to discuss here strategies to add it back and/or propose a PR.

[gberaudo]

Ping @fredj.

[ahocevar]

This is a mandatory feature of the initially funded implementation and needs to be added back ASAP.

[ahocevar]

Any update on this?

[gberaudo]

I could not get time to work on this as it is used by none of our clients.
@ahocevar, do you have time to work on this?

[ahocevar]

@gberaudo The drag box functionality was contract work paid by Boundless and conducted by Camptocamp. I understand that there have been concerns on the Camptocamp side about this component, but it is a hard requirement of Boundless's client to have it. It will be hard for Boundless to fulfil maintenance for their client with that core component gone, and I do not have time to add it back.

[gberaudo]

I think you should get in touch with @ebelo to see what can be done.

[ahocevar]

Thanks @gberaudo, I just sent an e-mail to @ebelo to see what our options are.

[ahocevar]

Looks like there is no way for now to add it back. Let's leave this open, maybe someone will be able to contribute it some day.