Outsource build (2): interfaces + gazeboserver/plugins

[varhub]

Outsource build (2)

Refer to #236

Changes:

• gazeboserver/plugins
• src/stable/interfaces

Fixes:

• Use ${CMAKE_CURRENT_BINARY_DIR} for all generated objects
• Use correct namespaces for .ice files
  from:

#include <common.h>
module jderobot {

to:

#include <jderobot/common.h>
module jderobot {

Therefore, include_directories() must only include cpp root (maintain old for backward compatibility)

• Full rewrite of slice2xx to allow complex hierarchies (modules==file tree)

Unresolved issues:

• slice2py syntax is odd. It realizes a flattened generation plus hierarchical __init__.py
  By the way, same problem was happening before, so it maintains exactly same format than before.
• module hierarchy is weird, (refer to java tree), interface jointmotor is not part of jderobot

module RoboCompJointMotor{

instead of

module jderobot{
module RoboCompJointMotor{

Tested:

• cpp (compile + quadrotor)
• python (introrob_py)

Video demo:

http://jderobot.org/store/varribas/uploads/videos/tfm-pretty-cmake.mp4

[varhub]

Please @fqez, test it when you have time.

[fqez]

Tested!