Couple of improvements

* Center image on the canvas
* Fix bugs with up, down and jump functions
* Fix bugs with first line disappearing
* Add scrollbar to file browser
* Add warning when number of iterations is too high to prevent freezing

Signed-off-by: Yaşar Arabacı <yasar11732@gmail.com>
Update examples

* Add ormanlik-daglar
* Add sierpinsky without gaps
* Add spiral

Signed-off-by: Yaşar Arabacı <yasar11732@gmail.com>