Restructure docs to separate package overview from tutorials

[cnmy-ro]

The new format could be of the following form:

- Home
- Installation

PACKAGE OVERVIEW
- Commandline Interface
- Projects
- Datasets
- Architectures and Loss Functions
- Engines
- Configuration System

BASIC TUTORIALS
- Getting Started with aerial2maps
- Creating and Running Your First Project
    -- Writing a Custom Dataset
    -- Adding a Custom Loss to CycleGAN

ADVANCED TUTORIALS
- Writing a Custom GAN Architecture from Scratch
- Using Custom Generator and Discriminator Architectures