Refactor start_data

[bomzheg]

for example copy all start_data to dialog_data or use ChainMap.

getters and handlers will get data from only one source - dialog_data

[Tishka17]

We need something that could be returned back to on_process_result. So dialog can distringuish different child dialogs. But it's obviuos that we should merge passed other data to dialog_data