Update libraries used in the project

[at15]

currently following libraries are used in Ayi

• console application https://github.com/codegangsta/cli (was renamed to https://github.com/urfave/cli)
• config https://github.com/spf13/viper
• error https://github.com/go-errors/errors

and they will be updated to

• https://github.com/spf13/cobra because it's from the author of viper
• viper won't change, but may need to specify version in glide
• https://github.com/pkg/errors since the old package is not longer active

also some new libraries will be introduced

• https://github.com/GeertJohan/go.rice or https://github.com/jteeuwen/go-bindata to embed assets in the program.
• https://github.com/stretchr/testify make testing in golang easier

TODO

• [ ] remove all old code since errors and cli are used in almost every file
• [ ] add new dependency
• [ ] fix test

[at15]

For cobra

• go get -v github.com/spf13/cobra/cobra to get its command line tool

[at15]

Finished in #40