Add `Keep Memory and World Info` option to New Session

[one-lithe-rune]

Motivation

Switching on edit mode, selecting everything, and then deleting, whenever I want to restart story generation from the beginning, or forgetting to do that and losing my just made edits to Memory (or World Info), has gotten tedious enough that I broke down and implemented an option to keep them.

Changes

• Adds a Keep Memory and World Info checkbox box to the new session dialog, defaulting to unchecked.
• Updates restart_newgame with an optional keep_memory argument, defaulting to false.
• Call restart_newgame with keep_memory set from the checkbox selection when the New Session dialog is confirmed.

Possible Problems/Concerns

• Maybe it should be clear_memory for the function parameter, and have the not in the call?
• I've set the default to not keep memory, so you get same behaviour as the current version by default. However maybe keeping should be the default? It's what I want to do most of the time.
• Tested connecting locally to Koboldcpp, rather than Horde.

Screenshot

[LostRuins]

There's actually a shortcut for that! Just long press the "Back" button.

Does that satisfy your use case?

That said this seems useful too, so I can add this as well