Inefficient execution of PMD within eclipse

[adangel]

There are several issues currently:

• A new PMD configuration is used per file
• Each PMD configuration uses an own classloader for the auxclasspath. This leads to inefficient memory usage - the classloader should be shared within the project. This leads to OutOfMemory errors in bigger projects.
• No multi-thread usage is used, each file is executed after another. If we know, that we want to execute multiple files (e.g. a whole project), we could execute PMD once with the list of files. Via Report/Renderer we can still monitor the progress file by file.
• If multiple projects are in the workspace, the log messages don't indicate, for which project PMD is currently executed.