* Fix the shaders that used the old texture name

* Add a "reload" method in the abstract Shader class

* Provide a default material when none has been passed by the user.
  Otherwise, results are random.

* Provide log (warning or error) when something is wrong)
v0.5: The shaders using the old texture name are now fixed.

Provides a default material to prevent random results when user doesn't
provide one.

Errors and warnings are now logged.
Merge branch 'develop'