Update Dockerfile to work as a web server

[Spaskich]

Overview

This PR updates the Dockerfile to fix the following issues:

• the build process gets stuck at the 'Configuring tzdata' asking for geographic area
• at the 'Cloning into dynet' phase the build throws a 404 error because the eigen repository is no longer hosted on Bitbucket
• the Flask and ps4 packages are missing

Notes

The whole process on updating the Dockefile can be seen here - #119
Huge thanks to @tiberiu44 for his help!

Testing Instructions

• cd to repo-dir/docker
• Build the image docker build --tag nlp-cube:1.0 .
• Start the container docker run --publish 8080:8080 --detach --name nlp nlp-cube:1.0
• Open the following link in your browser - http://localhost:8080/nlp?lang=en&text=This is a simple test

[tiberiu44]

The build fails because of incompatible DyNet version. We will fix this, once we switch to the 2.0 branch. The pull request looks good to me.

[tiberiu44]

Thanks again for the contribution!

Cheers,
Tibi