Pre-adapted some of the widgets
Enabled mouse button handling
Changed Configurable class

It makes more sense to assign real attributes once
instead of searching for proper value every time attribute is requested
If given attribute has a setter then it will be used
Removed redundant assignments
Naming changes, refactored padding
Broke excessive lines
Adapted Image widget
Merged redundant Textbox class
Added constant module
Corrected children size calculation logic
Corrected typos
New feature, STRETCH width for widgets in fixed layout
Refactoring, removed redundant properties
Small change in mouse handler logic
Removed unnecessary loop break
If no space available on bar, set size of stretched widgets to 0
Background color for layout and inheritance for widgets
New feature, true transparency