Dynamic provision/prepare, plan templates, verbose/debug levels

• Implement executing the last run using --last
• Adjust support for modifying plan templates
• Add a way how to edit values in a new template
• Explicitly mention supported distros in the docs
• Convert provision/prepare into dynamic plugins
• Describe difference between --verbose and --debug
• Support fmf name references in docs, update spec
• Support multiple verbose/debug levels [fix #191]
• Remove forgotten 'Core' section from stories
• Implement Plugin.show() for a full dynamic support
• Improve the workdir handling in the Common class