Update tutorial with new TOC

In #93, we decided on a new table of content for the tutorial.

This is the TOC proposal:
* Quick start
1. Download
2. Define analysis scope:
* Intro to `projects.json`
* Intro to `setup.cfg`
3. Deploy and run GrimoireLab
* GrimoireLab Architecture and Data Workflow
* Data Sources Management
* The `projects.json` file: projects, data sources & repositories
* Adding and removing projects, data sources & repositories
* Contributors information management
* Identities and profiles
* Merging, adding and removing identities to profiles
* Editing profiles information: affiliation management
* Adding and editing organizations information
* Dashboard and data visualization
* Public and private access
* Dashboard, panels and visualizations
* Filtering, querying and searching
* Panels customization
* Enriched indexes fields (name, type and description)
* Editing existing panels
* Creating new panels
* Editing existing visualizations
* Creating new visualizations
* Adding visualizations to panels
* Exporting and importing panels
* Customizing public dashboard
* Data Consumption through Elasticsearch REST API
* Platform management and monitoring

I expect that the TOC will evolve over time.

Initial work is in a branch at: https://github.com/chaoss/grimoirelab-tutorial/tree/agamotto

The TOC proposed above has been already set (https://github.com/chaoss/grimoirelab-tutorial/blob/agamotto/_data/sidebars/home_sidebar.yml)

Next steps is filling in the pages and creating a pull request to the master branch.