GUI_Development better design and some fixes

[BrunoMontalto]

feat: server comunication to check if chat creation is succ essufl

chore: added types in classes attributes

fix: now chat previews and messages are both scrollable with mouse wheel

feat: chat preview of last message is now truncated if longer than 15 characters

feat: now Chat.append_message inserts messages in order

now the width of the side_panel is fixed

[BrunoMontalto]

I fixed some problems feat: previews updates after any message is received fix: now the error label shows up when chat creation is not successful feat: if chat creation is successful, the menu closes automatically