Allow System imports to Programs

Per story [60721290](https://www.pivotaltracker.com/story/show/60721290).  Extends the `systems` template so it has its own tree footer, which allows imports as well as standard create/map function.

New view functions added to handle importing to program and downloading the import template for import to program.

`SystemsConverter` generalized to handle the case where systems are imported *to* something; this was previously just an admin import.

Also includes a fix for `reduce` in Can.JS that was breaking things.