pin uritemplate to 0.6 because google-api-python-client does not work with with version 3.0 of uritemplate

/cc @kazuhiko @jerome 

/reviewed-on nexedi/slapos!134

The ngx_http_realip_module module is used to change the client address and optional port to the one sent in the specified header fields.

so that the client IP is no longer the frontend IP, so rack
attack won't be blacklisting fontend IPs

coreutils
imagemagick
poppler

- removes wkhtmltopdf entry ;
  as cloudooo has a hack to use wkhtmltopdf
  (see 8b49da34 in cloudooo repository)

- removes useless mimetype entries ;
  OnlyOffice entries were also defined in the generic_cloudoo recipe.

If there is no binlog in srv/backup/mariadb-incremental (ie : the parameter
incremental_backup_retention_days is set to -1), then the import script fails.
This should not happen as this script just updates some inline paths.
This commit just add a correct check on variables and files existence

Changing from dr-x------ to dr-xr-x---

It sometimes happend that buildout unistall/install the section with this recipe,
which remore storage_path file and recreate it. In most of cases this is not wanted
because the recipe is used to generate password, so that password will change when this
happend.
To prevent buildout to remove storage_path, I introduced a new option 'create-once'
which, when set to True (the default value) will not let buildout play with storage_path file
by returning None in install recipe. Also install won't remove the file if the size is not 0.

/reviewed-on nexedi/slapos!129