PY: show categories.
PY: store categories.
PY: properly join tags in EntriesModel.
PY: support qobject_cast for TagsLineEdit.
PY: support editing the Categories column.
PY: keep track of known categories in OperationsManager.
PY: support editing the categories in ops view delegate.
PY: properly update categories for ExpenseEntries.
Merge branch 'master' of github.com:0xd34df00d/leechcraft