devs: fix memory leaks when deleting coupled model

We remove the recursive algorithm and we reuse function in graph.
devs: remove EventList class

We remove the vle::devs::EventList class and the EventList.hpp file.
This class is just an std::vector with addEvent and deleteAllAndClear
functions. We replace the class vle::devs::ExternalEventList with a
typedef equal to:

	std::vector < vle::devs::ExternalEvent* >

We upgrade source code in vle::devs namespace to take into account this
change.

This patch breaks API of vle::devs::Dynamics externalTransition,
confluentTransition and output functions (closes #54).
cmake: add a default value to CMAKE_BUILD_TYPE

The CMAKE_BUILD_TYPE is empty by default with CMake. We now assign
CMAKE_BUILD_TYPE to Debug if the CMAKE_BUILD_TYPE is empty.
devs: fix memory leaks in Attribute

The vle::devs::attribute(std::string, std::string) function call the
vle::devs::attribute(std::string, value::Value) function instead of the
constructor Attribute. We remove the useless second function.
devs: remove useless function in Simulator

The internalTransitionConflict and externalTransitionConflict are old
functions and are never used. We remove these function.
devs: remove useless return in Coordinator

The Coordinator::run() function returns a ExternalEventList pointer
always equal to NULL and unnecessary. We remove this pointer.
vpz: cleanup API Conditions about Values

The vpz::Conditions and vpz::Condition have old rebuildValueSet
functions that are useless now in VLE. We remove these functions.
devs: ExecutiveDbg needs virtual function

The function inherited from vle::devs::Dynamics need to be virtual in
vle::devs::ExecutiveDbg class. So we add `virtual' to init, output,
internalTransition, externalTransition, confluentTransition, timeAdvance
and finish.
vle: use STL algorithm to cleanup memory

Improve the source code by using STL algorithms to cleanup std::map < x,
T* > and std::vector < T* >.
devs: add DTrace in ModuleManager class

We add DTrace in ModuleManager when we load (dlopen) and unload
(dlclose) shared library.
devs: cleanup ModelFactory init values

Ensure to cleanup the InitValues map before any function call (to avoid
exception).
vle: add debug static variable in events & values

We add two unsigned long integer in value::Value, devs::ExternalEvent
and devs::InternalEvent to count allocated and deallocated values. These
variables are public and only available if NDEBUG is not defined.