Add missing ZeroClipbpard SWF file

Flash support for ZeroClipboard is not working in project pages since
the SWF file is missing. There was a typo in the .gitignore file that
ignored "*.sw?" files.
Make the link to a project's forum optional

Omit the link to the forum if the project's metadata does not provide
a forum url
Delete links to forum.spring.io
Merge pull request #1126 from bclozel/gh-pages

* pull1126:
  Delete links to forum.spring.io
  Make the link to a project's forum optional
  Add missing ZeroClipbpard SWF file