data: parsing file dependencies

This change adds the node NODE_FILE to the graph and the edge EDGE_INCLUDE, which determine the dependencies between
files by parsing the include preprocessor directive. File nodes can be searched and displayed in the GraphView as file
dependency graph. The filter "file" allows for selecting all files. The file depency information is used on project
refresh do determine which files need to get reparsed.

src/lib/data/graph/Edge.cpp

@@ -141,6 +141,8 @@ std::string Edge::getTypeString(EdgeType type) const
 		return "template default argument";
 	case EDGE_TEMPLATE_SPECIALIZATION_OF:
 		return "template specialization";
+	case EDGE_INCLUDE:
+		return "include";
 	case EDGE_AGGREGATION:
 		return "aggregation";
 	}
@@ -270,6 +272,13 @@ bool Edge::checkType() const
 		}
 		return true;
 
+	case EDGE_INCLUDE:
+		if (!m_from->isType(Node::NODE_FILE) || !m_to->isType(Node::NODE_FILE))
+		{
+			break;
+		}
+		return true;
+
 	case EDGE_AGGREGATION:
 		if (!m_from->isType(typeMask | variableMask | functionMask) || !m_to->isType(typeMask | variableMask | functionMask))
 		{