Changed length validation, typo fix

[maximmax42]

• Changed length validation from being byte based to character based (except for button labels, for some reason). Strings' max lengths should be not in bytes, but in characters #218
• Changed button label length limit to 31 bytes, because using 32 bytes exactly causes presence to not show to others, only to yourself. [BUG] Presence doesn't show for others when there's a button with a 32 symbols long label #182
• Also fixed a typo in the bool operator.

[Lachee]

LGTM