Big rewrite (not done yet)

* SDL2
* png instead of bmp
* resizable window
* much cleaner code
Remove some files.
Buttons and the stick work now.
Init video and joystick at the same time.
Set hint to allow inputs when the window is in the background.
Set logical size and reset window size when you press s.
Start using Controller_part
Rename img/default to img/n64.
A lot of changes.
Use the n64 directory.
Add sign variable and plus sign to config file.
Hat works!
Now things almost work a little bit.
Add the real parts
Add direction to hat.
Move action to Real_part.
Fix some things to make axes work.
Now axes work correctly.
Add treshold and change how Conf::get_int works.
Remove buttonmapper because it doesn't work with the new config.txt.