Refactor the Package database to include cmake and plugin information

[schmerl]

The CMake and nodelet handling is a bit of a fragile mess. The CMake files are parsed on demand - they should probably be included with the package database. This refactoring should include:

• Rewrite the CMakeLists.txt parsing code to something more akin to the XML parsing in LaunchReader
• Store CMakeLists.txt information in a datastructure and provide processing APIs to derive different targets that would be built
• Change the Package class to include CMakeLists.txt information
• Include package.xml information in the Package information
• Process node_plugins and other imported plugin,xmls and add