Add interval property

[paulvarache]

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I added an interval property to allow the user to choose when the watcher checks for change

[knolleary]

Hi, thanks for this.

Please have a read of our contributing guide in the main node-red/node-red repository - something we ought to have a version of in this repo.

Essentially, we prefer things to be discussed via issue or mailinglist before a pull-request is raised so that we can agree if the if the desired functionality fits in with what we have planned and what is being worked on.

The bigger item is that we also require a signed contributor agreement before we can accept any PR. Full details in node-red/node-red/CONTRIBUTING.md.

On this specific issue, assuming we resolve the points above, the interval presented to the user should be in minutes - not milliseconds as the underlying code uses.

Let me know how you'd like to proceed.

Nick

[coveralls]

Coverage increased (+0.01%) to 75.47% when pulling 4056a08b888d0736288a403a58e8d4a89c5d7883 on paulvarache:master into f8650bdb950cf1aa004a797241b513bfa2ba6580 on node-red:master.