Create 'editor' role in code (rather than config) to avoid Features issues

Currently, the 'editor' role is created via config in the panopoly_core module.

However, this can cause some problems with Features:

1. We don't want reverting panopoly_core to reset the permissions to their original state
2. Even though it's fine for a profile to override a config yaml from a module, there's a long-standing Features bug that makes Features act strangely when you try to do it: #2668562: Not detecting overrides in profile config files

Instead, creating it programmatically in hook_install() will eliminate these problems.