Post Beaker 0.15 site updates

- recorded release date for 0.15.1
- adjusted projected release dates for 0.16 and 0.17
- noted scoped of 0.17 may changed now we brought the loan
  management CLI forward to a 0.15 maintenance release
- updated tech roadmap
- moved development lifecycle preamble from the Handling Large
  Installations proposal to the new dev lifecycle section and
  updated it to reflect current practice

Change-Id: I3fa7fc79a5a231ee95206dc43ba867c75c7d10b8
Merge "Post Beaker 0.15 site updates"