Decoupling

- Eliminated some calls to context.config from Task‥cpp, reducing the coupling.
  If context can be eliminated from Task.cpp, via statically initialized
  variables, then Taskwarrior and the task server can share Task.{ḩ,cpp} which
  would be an enormous saving in effort.
Performance

- It it not necessary to make a copy of all configuration variable names, if the
  Config::const_iterator is sufficient.
more accurate .pot generation

- preserve notes for translators
- take sgettext into account
regenerate task.pot with notes
batch process es.po
batch process it.po
commands: fix some pluralizations
update es.po
fix typo
update it.po
Merge branch '2.3.0' of tasktools.org:task into 2.3.0