Split .config.json into separate files

[knolleary]

• New feature (non-breaking change which adds functionality)

Proposed changes

The runtime settings are currently stored in ~/.node-red/.config.json. This contains:

• the list of nodes discovered by the runtime
• user settings (eg editor settings such as 'show grid' etc)
• project settings (active project, list of available projects etc)
• other things - notable _credentialSecret.

Putting all of these things in one place is not ideal - a consequence of the Storage API only having a simple read/write API for the whole settings object.

This PR changes the default LocalFileSystem storage plugin to split the settings into 4 files:

• .config.nodes.json - the node registry
• .config.users.json - user specific settings (eg editor settings)
• .config.projects.json - project settings, including the active project
• .config.runtime.json - everything else - most notable _credentialSecret

This reduces the blast radius if any one of the files is lost for some reason.

It also means:

• a user can be more selective over what they backup. For example, they can backup the users file to save their editor settings, without also pulling in the _credentialSecret from the runtime file.
• when updating a setting, only the relevant file needs to be updated - we don't have to rewrite the whole file every time.

With this change, we will leave the existing .config.json in place. The logic is:

• if .config.json exists and .config.nodes.json does not exist
  • migrate .config.json to the four new files
• if .config.json and .config.nodes.json both exist
  • check modification time of both files
  • if .config.json is newer, migrate it to the four new files
  • if .config.nodes.json is newer, don't do any migration - use the four new files that already exist

We will leave the old .config.json in place because it eases the path if a user chooses to downgrade to pre 1.2 - they won't be left with no projects/_credentialSecret etc in place. This is more likely during the initial beta period of 1.2. We will begin to remove the old .config.json file in 1.3 or 2.0.

[coveralls]

Coverage decreased (-0.04%) to 76.887% when pulling 96d81ef on split-config into 81dc3de on dev.