DSL: change container_type to extensible container

Late addition to DSL 1.0 (oversight in the roadmap)

References: #4688
Merge pull request #6068 from rolandwalker/container_dsl

DSL: change container_type to extensible container
add NCSA OSS license type

Used for example by LLVM.
Merge pull request #6071 from rolandwalker/license_ncsa

DSL add NCSA OSS license type