Index declarations for better performance

[bjansen]

When a project is imported, every .ceylon file is scanned for declarations, which are added to the project's index for later use. The problem is, the parser does not build the model, so we can't access the fully qualified type name. For the moment index entries are based on the simple name, which can lead to overwrites if two declarations in different packages/modules have the same simple name.

See org.intellij.plugins.ceylon.psi.impl.CeylonClassImpl#getQualifiedName