text: Title: Update deprecated regex sequences
  Body: ## Classification:
  
  Maintenance
  
  ## Version
  
  AutoKey version: develop  5963c7ceae668736e1b91809eff426a47ed5a507
  
  ## Summary
  
  The CI tests are warning about several deprecated regex sequences. We should find alternatives and replace them.
  
  The regex is one of the better-tested parts of the code in terms of unit tests, so we should be safe with what we change.
  
  ```
  lib/autokey/model/key.py:122
    /home/runner/work/autokey/autokey/lib/autokey/model/key.py:122: DeprecationWarning: invalid escape sequence \+
      KEY_SPLIT_RE = re.compile("(<[^<>]+>\+?)")
  
  lib/autokey/model/helpers.py:21
    /home/runner/work/autokey/autokey/lib/autokey/model/helpers.py:21: DeprecationWarning: invalid escape sequence \w
      DEFAULT_WORDCHAR_REGEX = '[\w]'
  
  lib/autokey/model/abstract_abbreviation.py:143
    /home/runner/work/autokey/autokey/lib/autokey/model/abstract_abbreviation.py:143: DeprecationWarning: invalid escape sequence \s
      if len(stringBefore) > 0 and not re.match('(^\s)', stringBefore[-1]) and not self.triggerInside:
  ```
  