Add some node support aliases

[shadowspawn]

Node is adopting some aliases to refer to useful combinations of release streams:

• https:/nodejs/package-maintenance/blob/master/docs/drafts/PACKAGE-SUPPORT.md#node-name-space
• Standard grammar/keywords to reference node release lines nodejs/package-maintenance#236 (comment)

At this point the information about what lines are active or still supported is not available in index.tab, so for this PR the aliases simply revolve to either the latest lts node version of the current node version. In the future nvh ls-remote could display multiple versions where appropriate.

• node support alias => nvh existing alias
• lts => lts
• lts_latest => lts
• active => current
• lts_active => lts
• current => current

See also more detail in: tj/n#617