New canvas widget. - [x] paint filled rectangles - [x] paint images (Tiles) on canvas - [x] more [mouse events](https://developer.mozilla.org/en-US/docs/Web/API/Element/mousemove_event), probably like HTML events: > The order of events related to the onmouseup event (for the left/middle mouse button): > > 1. [onmousedown](https://www.w3schools.com/jsref/event_onmousedown.asp) > 2. onmouseup > 3. [onclick](https://www.w3schools.com/jsref/event_onclick.asp) > The order of events related to the onmouseup event (for the right mouse button): > > 1. [onmousedown](https://www.w3schools.com/jsref/event_onmousedown.asp) > 2. onmouseup > 3. [oncontextmenu](https://www.w3schools.com/jsref/event_oncontextmenu.asp) - [x] paint theme elements on canvas - [x] access active theme colors