editorconfig: update to align with reality

Set the root = true flag, so tools don't continue traversing the tree
looking for more editorconfig files.

In practise we have Unix line endings so adjust the end_of_line flag and
enable UTF-8 charset.

Enable final newline for all files but patches - most editors already
insert one and git gets unhappy otherwise.

Finally, use 4 space indent for shell scripts... In practise their style
varies _a lot_ but this seems reasonable default IMHO.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>