Modify Rally docs (for readthedocs), sticking to the following principles:
* Make the docs structure as simple as possible:
1. Overview
2. Install Rally
3. Rally step-by-step
4. User stories
5. Plugins
6. Contribute to Rally
7. Rally OS Gates
8. Request a New Feature
9. Project Info
* Keep in mind what questions different target groups usually have about Rally.
The new structure relates to these groups as follows:
1 -> Managers
2, 3, 4 -> QA
5, 6, 7, 8, 9 -> QA & Developers
* Make each docs page to be easy to get through;
* Prefer pictures over text;
* Use hyperlinks to easily navigate from page to page;
* Fix incorrect English & typos.
Also add a sample for SLA plugins.
Change-Id: I720d87be851c273689a21aaba87fc67eacf0f161
30b1ad593f