Verify Gazebo + plugin installation

[Andrés Fortier]

Follow the steps detailed in the README starting with a clean repo clone (ideally would be to do this inside a fresh VM with ubuntu 14.04, but since we should be doing this with a docker image that seems to be useless). If any issues appear, fix them and update the install documentation.

Also, please include the required pointers to install Docker if the user doesn't have it already.

[Agustin Alba Chicar]

@andres_fortier:

• Docker container compilation has been tested and is working properly.
• Checked Manifold commit --> 5a095e0
• Checked Gazebo commit --> markers
• Checked volumes: terminus and rndf_gazebo_plugin
• Compilation of rndf_gazebo_plugin with #28

[Andrés Fortier]

Thanks @agalbachicar , feel free to close this when you consider it done.