Component locks; virtualenv/conda installation support

Component Locks

PR: #120

We have a lot of components, and not all of them are compatible with another. When scheduling experiments and designing specs it is hard to keep all of them in check. This adds a component locks that does automatic checking of all specs when importing, by using the specified locks in rl/spec/component_locks.json. Uses the minimum description length design principle. When adding new components, be sure to update this file.

• add double-network component lock
• add discrete-action component lock; assume continuous agent can handle discrete action spaces as a generalization

Improved Installation

PR: #121
Solves: #113, #114, #115

• fix broken gym installation. See gym PR 558
• layout installation steps in doc, use binaries for server setup
• introduce version lock for dependencies with requirements.txt, environment.yml
• support installation by system python, virtualenv, conda, integrate into Grunt
• add quickstart_dqn for example quickstart in doc

Bug Fixes

DoubleDQN

PR: #119

• restore missing recompile_model call to the second model in DoubleDQN.