Rename window titlebar functions to follow the general api naming scheme.
Fix certain elements not updating properly when text padding is changed.
Fix scrollbar alpha not updating properly.
Add listboxes.
Make sure the user can't modify default fonts.
Fix a null pointer crash in mgui_element_destroy.
Remove label size from the extended constructor, make the colour parameter a text colour one.
Fix label alpha not updating in some cases.
Fix a renderer font loader issue which broke bigger fonts completely.
Fix progress bar alpha issue.
Make sure window components (titlebar, close button) don't get added to the layering system.
Add basic fade effect to disabled elements.
Fix empty strings not being added to a memobox.
Move currently active element to the top.
Fix an OpenGL renderer crash when trying to load a bitmap with dimensions that are not a power of two.