rose edit: ignore rose-meta.conf root level confs.

Instead of dying with a traceback.
Merge branch 'master' into 473.edit.meta.root-settings
metomi/rose#311: tidy use of delimiters
Merge branch 'master' into 473.edit.meta.root-settings
Merge pull request #491 from benfitzpatrick/331.metadata-delimiter-doc

metomi/rose#331: tidy use of delimiters
metomi/rose#411: add new default metadata
metomi/rose#411: tidy
metomi/rose#411: opts
Merge pull request #481 from matthewrmshin/473.edit.meta.root-settings

rose edit: ignore rose-meta.conf root level confs.
metomi/rose#411: remove typo
metomi/rose#411: remove old option
Merge pull request #492 from benfitzpatrick/411.metadata-builtin

#411: add more default metadata