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.

Beginne mit der Durchsicht des bestehenden TOC in _data/sidebars/home_sidebar.yml und der anfänglichen Arbeit im agamotto branch. Verwende die vorgeschlagenen Abschnitte, um die Tutorial-Seiten zu identifizieren, für die noch Inhalte fehlen, überprüfe anschließend, ob die Seiten die aufgelisteten Themen abdecken, und erstelle einen pull request mit dem Ziel master.

Vom Indexierungsmodell aus dem Issue-Text verfasst.