Start providing package information in RDF

Provide a RDF/XML access to a package basic information using the DOAP ontology
Add a link on the /acl/name/<name> page to access these info
Add python-rdflib as a dependency

This library is needed for the semantic export(/doap/)
Start cleaning the pkgdb app

Clean up the root controller

Remove the specific controller
Remove layout, apps and builds templates and update the home page
Keep cleaning templates
Remove build box
Remove the search box for now
Revert "Remove the search box for now"

This reverts commit 56d3fb6b2a64aedfc8885f5ca19a8f564ab72f3a.
Bring back the _apps_search template trimed down to only search on packages

Adjust the home page to include this search box as well
Fix html tag and indentation
Layout fix in the search box
Fix the display of the help in the search box