Change repository flow

We decided to change repository flow to be more consistent with git flow. The steps to convert current content to new flow is as follows:

• change documentation (!346 (merged))
• rename v4.0 to hbk
• rename v4.1 to hbl
• rename v5.0 to hbd
• Mark hbk, hbl and hbd as protected branches
• set as default branch hbk instead of master
• drop master branch (preserve as something like future-6.0
• change HBK build branch to hbk on Jenkins
• change HBL build branch to hbl on Jenkins
• change HBD build branch to hbd on Jenkins
• merge hbk to hbl for initial consistency
• merge hbl to hbd for initial consistency
• remove jobs for master on Jenkins
• Review repository membership (promote to maintainers who has approve himself to understand and accept the workflow)