Move variablesection specific code to SsuVariable class
[log] Expose correct priority to journal
Move repo filter definition to repo manager
[variables] Add default sections, local variables, full recursive resolving

- variable section resolving now tries to automatically identify default
  sections when looking up a complete section
- local variables may be defined by prefixing with _ or using the local
  keyword
- multiple variable sections are now supported, as well as adding both
  the variables keyword and variable values in a section