Remove trailing blanks, add check step to keep code free of them

[strk]

@mloskot see how you like this

[strk]

See also how Dronie likes it: https://git.osgeo.org/gogs/geos/geos/pulls/2

[mloskot]

@strk

@mloskot see how you like this

If you ask me, it doesn't solve any of my problems.
It doesn't unify tabs/spaces, indentation, brackets placement, and <here long list>.
Besides, check step is covered by only one of two official build configurations.

You know my opinion, .editorconfig is no improvement to the current situation.
It is as just a small helper that has very little to do with formatting style of a complex source code.

However, I don't want to interfere, do what you like.