Create "Links" block for project nodes

What will be put in this block needs to be defined.
Do we add the possibility for the project maintainer to create any link (title+URL) he wants? (See "Add link" one the prototype.)
Some of the links contained in the bottom of a project page at present could also fit in here.

To keep a clear CSS, this, actually, will be a Drupal block.

Here is a first patch. "Home page" and "Try out a demonstration" links, if existing, are displayed.
We probably need to fill it with other links (what about documentation, browse CVS repository, license or changelog?).

Please leave any comment regarding code style and way of doing it. :)

I created the following issue to gather some project blocks:
#372580: Move the project node links to blocks

See #372580: Move the project node links to blocks.

This is blocked on #372580: Move the project node links to blocks.

See #425742: Add a mechanism to store custom links per-project about storing/adding new links. Let's just handle that separately, since it's a minor feature and shouldn't otherwise hold up progress here.

Now that #372580: Move the project node links to blocks is done, all this needs is a small patch to drupalorg_project to alter the project links for the 'resources' section to a) make it 'type' = 'block', and b) change the label to "Links". See also #371979: "Get Involved" Block on project pages for a similar task for a different block.

Linking this from the Redesign project #661550: Meta issue for Drupal.org customizations because this issue was tagged 'drupal.org redesign'

We can live with just putting things in the project node body.