Add custom (user) generators

• Add separate base class for word-based generators
• Add custom (user) generator support
• Refactor built-in generators

Complete configuration and alter default generators

• Replace default Markov pronounceable generator with gibberish
• Rename Dictionary generator module
• Add licence and licensing info
• Improve usage description in README
• Add generator descriptions to README
• Add strength bar toggle to configuration
• Improve filtering in configuration

Initial Release

See README for details.