extsubproj plugin : manages links to external subprojects on remote forges

For the moment, manages URLs that can be displayed in a widget in the project home page.

If the remote subprojects are on a FusionForge running the doaprdf plugin (or any compatible forge ;-), fetches the project's doap:name dynamically to render the link.

TODO : provide compact-preview of the remote projects

Note : may be interfaced with extratabs to provide each sub-project with its own tab, in mostly empty super projects otherwise

This project was implemented in the frame of the COCLICO project as a POC of distributed forges (WP2).