Fix a few problems with `volt precompile`, and enable cleaner ERB templates.

This fixes:

* Generation of an apparently spurious, and entirely empty `assets/components/main.js` (as opposed to `components/main.js` which is generated properly).
* An error caused by `TaskHandler` not being loaded when needed.

Additionally it enabled the use of `<%-` and `-%>` in ERB templates, allowing control over generated whitespace.