- Added 'Layer::OnEvent()', 'Layer' now handles an event by itself and
doesn't need another class to determine the event's type
- Added reverse iterators 'rend()' and 'rbegin()' to 'LayerStack'
- Removed 'LayerStack::On*()', 'LayerStack' is meant to be a data
structure for the layers,
- 'Layer::On*Event()' are now protected and called by 'Layer::OnEvent()'
- 'Application' now handles iterating through the 'Layer's
and calling the update/on* functions
- Fixed a typo where in 'Mirror' where the name of the 'MirrorLayer' was
"SandboxLayer" instead of "MirrorLayer"
- Added 'Camera::OnResize()' for keeping the aspect ratio updated to
prevent streching/squashing the scene
- Added 'FrameBuffe::Resize()'
- Enabled ImGui docking and viewport
- 'MirrorLayer::m_Camera' & 'MirrorLayer::m_Framebuffer' now adjust their properties
when ImGui's available region changes
