The Origianl Mobility and ewsn11_cooja_interference Plugins (Authors:Fredrik Osterlind, Marcus Lunden, Carlo Alberto Boano) were built on Contiki 2.4, after that the directory structure was changed , because of which these plugins were not getting built. Here are the working PLugins for Contiki 2.7 after making the necessary changes. I have not checked the functionality of the patch on Contiki 3.x, as a result I am not sure about the directory changes in 3.x.
Issue pull request to modify it for 3.x.
*Make sure you change the Build.xml file path to link the Cooja.Jar file in Cooja_Jar Property.