Add link to a separate assets repository

[Tzky]

Once the SpongeAssets repository becomes available to the public, this PR will adjust the Art Assets page to redirect users.

Solves #457

[Spongy]

A preview for this pull request is available at https://cdn.rawgit.com/Spongy/SpongeDocs-PRs/f62dac32/index.html.

Here are some links to the pages that were modified:

• modified https://cdn.rawgit.com/Spongy/SpongeDocs-PRs/f62dac32/about/assets.html

Since the preview frequently changes, please link to this comment, not to the direct url to the preview.

[Tzky]

I'm not sure if we should keep the usage rules on the Docs or not as they'd better fit on the new assets repo.

Thoughts?

[Inscrutable]

The usage rules should get reviewed when the new repo is ready to go public, but I don't see the harm in having it reproduced. That way they will get translated, and if this is the staging point directing people there, then keeping them is still appropriate.

[Tzky]

Agreed. I'll keep them, but they must be updated before we pull this PR in.

We should also pull this PR into the static branches, not much extra effort, but keeps things clean.

[Inscrutable]

We need to determine what license we're using. I think it'll be Creative Commons (CC0) or possibly CC-ND (non-derivative) or even CC-NC (non-commercial)�. I'll let the overlords decide that one.

[meyerzinn]

Any update on this?

[Tzky]

We're still working out the details of the SpongeAssets repo. Afaik it's a private repo currently.

[Tzky]

Bump. With the relicensing of the docs currently in progress, we should get this resolved too. Are there any plans to get a repo up with all assets?

[Inscrutable]

This ancient PR needs a clean up if it's ever going to happen.
The assets repo in the link does not exist, and in any case I think we should largely replace the contents of the page with excerpts from and a link to the Sponge Branding Manual. Anyone want to help here? Someone's arm needs to get twisted to get the manual formally approved, and I note that it's content is not quite in keeping with what the docs say at present. We also need to find or create new links to master graphics assets, if we're ever going to officially offer them.
Pinging the absent @Tzky

[kashike]

[Inscrutable]

This is currently a dead duck until @Mumfrey gives it some love.
A new PR can get made when that eventually happens. Or ragnarok.

[ST-DDT]

I added most of the stuff from everything till b898b28 in #776