fix & document template library folder and type #1702

[mblackstock]

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Proposed changes

Changed template node to use correct library name and type (templates/template) and documented instructions in the node documentation info.

While templates saved in the library will be orphaned, there is not an easy solution for allowing users to migrate their templates from the current functions directory to the templates directory for a number of reasons:

• node runtime does not have access to the library
• lazy migration using the front end (e.g. open both libraries, save only to templates) would not be worthwhile considering the changes involved, the number of users this may effect (few?)
• could write a migration script, but would be difficult to get right since code would need to distinguish between templates and functions.

Checklist

• I have read the contribution guidelines
• For non-bugfix PRs, I have discussed this change on the mailing list/slack team.
• I have run grunt to verify the unit tests pass
• I have added suitable unit tests to cover the new/changed functionality

[coveralls]

Coverage remained the same at 87.755% when pulling abfe88d on SenseTecnic:fix-1702 into 2534530 on node-red:master.

[knolleary]

Can we remove this text? My assumption is this will affect a pretty small set of users so would rather not tarnish the node info with this. We can make sure it is highlighted in the release blog post.