Honor output range distribution in dash::transform

[devreal]

1. Implement global-to-global dash::copy, needed for
2. dash::transform that honors the distribution of the output range for local input ranges, which
3. now also works with std iterators, .e.g, coming from std::vector

Fixes #386

[fuchsto]

@devreal I merged your changes into PR #410 to fix this on a "substantial" level using views / ranges, your unit test are especially useful for this.

[devreal]

Perfect, thanks a lot!