add "timers" types to known types

[Steve-Mcl]

fixes #4102

Types of changes

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

Proposed changes

Ensure serverside function node editor gets a ref to the "timers" types

Checklist

• I have read the contribution guidelines
• For non-bugfix PRs, I have discussed this change on the forum/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: 68.609%. Remained the same when pulling 97fbad4 on Steve-Mcl:add-missing-timer-types into 586006d on node-red:dev.