[MNGSITE-548] Update subproject guide to new term

[Bukama]

This PR updates the guide for multi-project setups to the new term "subproject".
It also consistently uses lowercase for the term subproject(s) in headings (except the page header).

[elharo]

How do we redirect from the old URL to the new URL?

https://www.w3.org/Provider/Style/URI

[Bukama]

How do we redirect from the old URL to the new URL?

https://www.w3.org/Provider/Style/URI

Readded the old page with a link to the new one.

[cstamas]

How do we redirect from the old URL to the new URL?

https://www.w3.org/Provider/Style/URI

See https://github.com/apache/maven-site/blob/master/content/resources/xsd/.htaccess
We already do that for XSDs

[slawekjaranowski]

How do we redirect from the old URL to the new URL?
https://www.w3.org/Provider/Style/URI

Readded the old page with a link to the new one.

You should add redirect to: content/filtered-resources/.htaccess instead of page

[slawekjaranowski]

Can we try to use puml for it?

[Bukama]

As my experience with puml is quite limited as of now, I would like to tackle this task while supporting you on #482.

But you are the boss :) I can try to do this after xmas.

[slawekjaranowski]

picture is not an issues, can be improved later.

[Bukama]

How do we redirect from the old URL to the new URL?
https://www.w3.org/Provider/Style/URI

Readded the old page with a link to the new one.

You should add redirect to: content/filtered-resources/.htaccess instead of page

Thanks for the hint, updated (and removed the old one again :D )

[Bukama]

Thank you @elharo for pointing me to the mistakes. Fixed them

[Bukama]

Added @elharo suggestions and rebased (to resolve htaccess merge conflict)

[jira-importer]

Resolve #1130