Bug 12545: Add EditorConfig.org file to the source tree

Bug 12545: Add EditorConfig.org file to the source tree

This patch adds a .editorconfig file to the source tree, that
enforces some of our coding guidelines.

Some editors try to detect the desired configurations from the currently
opened file. As we have tons of old code that doesn't follow our current
coding guidelines, this can lead to unintended QA problmes.

To test:
- Apply the patch
- Verify the .editorconfig file is in the top-level directory
- See the .editorconfig file expresses our coding guidelines

Regards
To+

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>