[feat] #111: change functions to handle amounts list.

* modify
    * handle_intpermediary_transaction(),
    * generate_and_send_transaction(),
    * generate_transaction_document()
* all will now use tx_amounts list

* create a unit test for generate_transaction_document()
* create a patched head_block() function.

/!\ the created patched function does not return a whole fake block, only relevant infos for now.