Adding 'Data storage and preservation' section

[c-martinez]

Adding data preservation section, written by @vincentvanhees and discussed on data-sig.

[c-martinez]

@jiskattema -- could you have a look to see if you agree with the chapter as it is at the moment?

[vincentvanhees]

Jisk and I discussed and agreed on some initial changes:

• Add a statement that when privacy sensitive data is involved you should contact the privacy officer. If you are not sure then also contact the privacy officer.
• Remove all other statements about how to handle privacy sensitive data.
• Remove the statements about ring of trust, because they are irrelevant for data preservation.
• Clarify whether it is good to zip or not zip data, possibly tailored to type of user.
• Mention data management plan

I struggle to find time to do this at the moment. Maybe I will be able to do it later this summer.

[bouweandela]

Merging for now, if there are any issues remaining, please create an issue and pull request to resolve them.