Bug related to the conflict between the deletions of UIData and GLViewer solved by the mean of Qt signal/slot mechanism.

Stack mechanism added to UIMainWindow in order to change its central widget by saving and restoring the previous one.

Gradient widget modified so as to manage correctly the displacement of stops using the keyboard input in the case of multiple stops with the same values.

Function added to DisplayableInterface enabling to load the content of a resource file to a QString.

Gradient widget modified so as to manage correctly the displacement of stops using the mouse in the case of multiple stops with the same values.

Callback function added to UIMainWindow to trigger events when the selection in the project view changes.

Performance counter activated when F12 is pressed.