Dewi-core

- fix package requirements in setup.py
- start using semantic versioning

- !!! DEWI goes into multiple repositories and packages
- use only 'protected' members with single leading underscore ('_')
- MainApplication: argparse.Namespace object's 'protected', custom
members end with '_' instead of leading '_', as they are touched
from MainApplication and can be read anywhere
- Plugin: add '_r()' for simpler command registration,
removed default depenency - it's empty list
- Keep logger, config, plugin, and MainApplication classes with their
dependencies, others are in different packages

- MainApplication: --debug implies --log-level debug
default log level: info
- images/filedb: add count() to count entries in photo_file_info table
- images related commands: use exiftool-5.26 as MacPorts updated it
- safe_delete_images: handle Exceptions at unlink(), mainly PermissionErrors
- add further log_*() calls into dewi.rrdtool & realtime_sync

- pretty-print output command list (e.g. 'list-all')
- add dewi.utils.archive, which contains an UnZip class to (partially) unzip
.zip files
- if a command is mistyped or non-existing, print at most 6 similar command
names, or list all of them
- dewi.images.filedb: add rollback() method to FileDatabase
- dewi.core.context: Context got 'commands' and 'command_registry'
properties, and always contains the corresponding 'commands' and
'commandregistry' fields
- introduce dewi.core.logger module, log_debug, log_info, etc. can be used

- fix setup.py

- add Connection class and ensure_connection() method to kayako module
to reuse calculated signature and provide an object for easier testing
- config/node: add NodeList and also test the module
- rrdtool: use NodeList & fix modifiers
- NetworkCardVendors: add option to prevent network usage
- logparsers: add support to add multiple callbacks to a pattern:
during log processing one pattern matching - multiple calls.
And ensure that '\n' (0x10) is handled only as log line separator
- add lithurical command to print events of a calendar year
- kayako: add TicketStatus and TicketStatuses classes