Lazy /Conditional loading of 3rd party Quantum libraries

[rajibchakravorty]

Lazy load/Conditionally loads 3rd party libraries : qiskit, pyquil and cirq.

Based on our discussion, change made from the draft PR earlier:

1. opencontrols still will have all the external libraries as dependency - this implies that those libraries are still installed when user installs opencontrols as opposed to user installing those separately.

2. Removed all package load/import error checks. This is because the 3-rd party libraries are still part of the dependency list in `opencontrols'. In that case, there is no change in behaviour whether the libraries are imported at the top of the module or inside a method within the module. The separation of.

Notes

1. Added pylint: disable=too-many-variablesin a couple of places - the solution is known; wanted to concentrate on library loading in this PR [that and a couple of other minor changes will be made in successive PR]
2. When importing cirq modules in this fashion from cirq import .... instead of import cirq followed by cirq...., pylint somehow complains and could not find a solution. Any suggestion is welcome there. Not a major issue, but somehow breaks the pattern compared to what is done in other libraries.

[charmasaur]

When you say "pylint somehow complains and could not find a solution" regarding the cirq imports, what exactly is it complaining about?

In any case, this seems fine to me. Don't get me started on the "too many locals" check -- I think it's pretty silly, so fine to disable.

[michaelhush]

I'm going to remove myself as a reviewer, as I don't understand what the purpose of this PR is anymore.

If you haven't removed the qiskit, cirq and pyquil as dependencies in the install. Then I wouldn't call this lazy loading, indeed I don't really know what the point of this is.

Nevertheless if this is somehow helpful for getting this dependency review fixed in the short term then I'll leave this up to @charmasaur and @rajibchakravorty if you want to pull it in.

In order to keep track of the other minor issues that have popped up after this PR, I would recommend you make tasks in back log on Jira @rajibchakravorty.