Added a separate content type for .v files

This commit also adds a Coq-specific icon -- and an association with this
new content type -- to the Coq editor
Added a dedicated Coq perspective

At the moment, this is just a vaguely-appropriate view arrangement
Use the Coq icon for the goal viewer
Stopped using the deprecated org.eclipse.ui.actionSets extension point

Using org.eclipse.ui.menus for this also provides automatic binding hints,
which is nice
Merge pull request #10 from ale-f/project-infrastructure

Project infrastructure
some updates
Merge pull request #11 from ale-f/project-infrastructure

Stopped using the deprecated org.eclipse.ui.actionSets extension point