Create a standard sidebar structure in layout.html

[javabster]

The layout.html should have a standard structure that can be pulled in by all qiskit repos.

Current plan:

[language dropdown]

[search box]

Qiskit {Repo Name} Documentation
   Overview
   Getting Started
   Tutorials
   How to Guides
   API Reference
   FAQs
   Release Notes
   GitHub

[previous releases list]

Open questions for discussion:

• Should we require every page listed above or just some or none?
• Which pages should we insist be there and which should be optional?
• Should we allow individual repos to add their own links to the sidebar list?

cc: @HuangJunye @agebbie

[javabster]

Updated standard structure from discussion today:

# Standard - Must haves
Overview
Getting Started (installation + hello world + link to tutorials)
Tutorials
How-to Guides
API Reference
Explanations
Release Notes
GitHub

# Standard - recommended but not mandatory
Previous Releases

# Optional Extras
blank box we can fill with optionals e.g. FAQs