Add a way of exporting builds?

[pazdera]

The builds are being stored inside the repository tree that isn't set up to be browsed by users. But sometimes it would be nice to build a package and export the *.deb outside of there without having to search through the repo tree manually.

A subcommand like this would be useful:

dr export <package-name> <build-version>
dr export <package-name> release           # exports the version from release
dr export <package-name> devel             # exports the version from devel
dr export <package-name> scratch           # exports the version from scratch

Examples

dr export make-snake 1.3-1.2015-05-06build1
dr export make-pong release
dr export make-minecraft scratch

What needs to be done

1. Add the export subcommand into the Thor command class.
2. Add a function to retrieve the path to the build into Package class.
3. Use the function in the new subcommand to copy the file from that path to the current working directory.