Add context menu item to center view on the scene editor

[AlexandreSi]

Add new methods to:

• ✅ Return to initial position (view matches the game resolution)
• ✅ Fit zoom to selected instances (center of the rectangle that contains them all
• ✅ Fit zoom to the whole scene

Technical side quests done:

• Use Rectangle class everywhere the former rectangle object ({x, y, width, height}) was defined
• Remove deprecated keyboard shortcuts class
• Add missing types a bit everywhere it was needed (mainly for instance measurer)

Notes:

• There was a condition that prevented to detect mouse mid button clicks in the deprecated keyboard shortcuts class for Mac-like machines (that prevented to move the scene keeping the mouse mid button pressed) => I didn't keep it