Add walk through examples in documentation

[lzpap]

Related: #268

Extend pyota documentation with well explained code examples for common use cases. Take inspiration from the python community workshop.

Suggestions for code examples are welcome!

Besides the basic examples of sending and receiving data or tokens, try to show useful "modules" for application developers.

For example:

• code snippet to gather all funds for a seed and send them to a new, unused address
• put JSON-encoded sensor data on the Tangle and fetch it from there
• etc...