Fix javadoc warnings for unknown tags

@sine -> @since

@lnk -> @link

@author: -> @author

Make embedded @ sign literal in one case where it is literal
Remove trailing extra curly brace from javadoc @see reference
Use javadoc @see external URL syntax for these external URLs
Remove empty @see javadoc comment in UpdateCenter
Terminate javadoc @link tags with curly brace instead of right paren
Merge pull request #860 from MarkEWaite/javadoc-fixes-1

Javadoc fixes for Jenkins core