First steps towards having a "w3af" module:
 * Created directory and moved core and plugins inside
 * sed replaced all imports, ie. "from core." => "from w3af.core".
 * Modified some hard-coded path references in the source
 * Modified w3af_console and w3af_gui to "work"

Still need to keep working in order to have a GUI and console startup.
Then need to run all unittests, many things will fail for sure.