Remove duplicated documentation from docs and wiki

[stefanodavid]

There are duplicate pieces of documentation in docs and wiki that we need to deal with. In this issue we

• [x] rename Resources for developers section
• [x] rename and move to Howto section GITHUB Quick Documentation for Contributors. Change also the link from wiki.
• [x] rename guidelines' bignami version to "quickstart guidelines" or similar
• [x] improve wiki's introduction text
• [x] remove full guidelines from docs and link them from within "quickstart guidelines" (to be discussed further)
• [ ] remove (outdated) howto How to set up your local Development Environment? (to be discussed)
• [x] TBD

Note that FAQ are subject of a separate issue #255