Why
Many mods have their own entities.In the past, if we needed to switch the entities, we need use the mod's entities.png to take the vanilla entities.png. Also, it spent more time to switch entities.
This PR solve that problem, be different from DDNet, mapper put their entities images in %APPDATA%/editor, and they need to press this button to open a file dialog
!图片
Then they could choose ...
The old editor use middle mouse button to move view,
Also, many image processing software set this button to move view by default.
Right mouse button still could to move view
