The 'about.html' file in 'bin' directory should not be executable

At !73 (comment 10795), @ahofkamp noted:

There is an executable bin/about.html file. It looks more like it should be in the root directory to be honest.

In products/org.eclipse.escet.product.headless.feature/build.properties we set bin/** permissions to 755. We should not do this for the about.html file.

I hope adding an entry after it for about.html to set it to different permissions allows us to keep bin/** for all the other scripts, such that we don't have to list them individually.

Note that we must keep the file there, see !73 (comment 10813).