Add reserved namespaces

[rubenwardy]

Idea by @Warr1024

3.3. Reserved namespaces

A reserved namespace is a prefix to a package name like abc_, where any package names that begin with that prefix need permission from the namespace owner to be used.

You can request a namespace be reserved by opening a thread on a package that uses it. A namespace must be in active use and must be specific enough to have low risk of conflict - for example, mobs cannot be a reserved namespace. The package must also be deemed "serious" enough to get a reservation - larger and more longterm projects are more likely to qualify.

Mod names used in packages posted on CDB or the forums before 2020-07-15 are exempt.

List of reserved namespaces:

• nc_ is reserved by NodeCore.
• ikea_ is reserved by IKEA.

[erlehmann]

Please make it so that mcl_ can not be reserved, as there exist three related projects (MineClone2, MineClone5. Mineclonia) and several independent mods that use the prefix.

[rubenwardy]

Forks will be able to use the same namespace