Filetransfer

- Drop support for ftputil 3

- Replace salmagundi.config with easimpconf
- New: option keep_alive in host configuration

- New: option dir_a_option in host configuration
- Now works with ftputil version 4

- Pin dependency ftputil to version 3.4 because of incompatible changes in version 4.0

- New: options log_level, retries and ready_file in job configuration
- New: single_instance in job configuration can be set to arbitrary lock name
- Changed: JobResult.file_list tags are now FileTags enum members
- Changed: function configure() returns JobResult object and status code
- Changed: return/status codes of filetransfer script and exceptions
- Changed: names for entries and placeholders in custom email configuration

- New: option single_instance in job configuration
- New: logging can be disabled in application or job configuration
- Add function set_sigterm_handler() to API
- Upgrade dependency: salmagundi -> 0.11.2
- Bugfix: error when sending email if file list contained source or target errors