Clean-up and replace Intellectual property chapter

[egpbos]

• Add a section to Best Practices.
  • NLeSC-internal note: refer to the PMP, section "IP policy"
• Remove the chapter: PR together with licensing
• Afterwards: check for broken links (globally! the PR link checker only checks changed files...)

[egpbos]

Because of the NLeSC-internal reference, this should wait until #394 is merged.

[egpbos]

#394 is merged, this issue is unblocked.

[egpbos]

This should actually be merged into licensing, will add to #401...