Replace glide with dep

[tariq1890]

This PR uses golang dep for dependency management.

i) Updated Readme to point to Dep instead of glide ii) Update Makefile to run dep ensure iii) Added new Makefile function dep-check which runs the dep check command. dep check is a lightweight validation mechanism to ensure the dependencies are managed correctly within the repo

[ian-fox]

Admittedly I haven't been keeping up as much with go this term as I should have, but hasn't dep been superseded by https://github.com/golang/go/wiki/Modules?

[tariq1890]

yes. Modules is going to be the de facto standard for package management I believe