Bookmark feature

[jerojero]

User story:
As a player I would like to have the ability to add bookmarks that would allow me to reset all moves to the time the bookmark was placed.

Implementation:
The way this would work could be as follows:

1. There is a button to add a bookmark besides the pause button
2. A new bookmark is placed, user can continue playing normally
3. There is a button on the bottom that brings up the bookmarks
4. When a bookmark is clicked, all moves done are reset to that point

Rationale:
In a way, you can think of the bookmark feature as a "save state" for the board. Placing a bookmark after already having bookmarks wouldn't affect any previous bookmarks, you can freely move between them.

This allows for users to much more safely navigate through games where at some point you need to take a gamble on what a potential number could be (that maybe, much later on ends on an inconsistent board state). Right now you can use the "back button" but you might have forgotten at exactly which point you made the change.

I think having two buttons, one to place the bookmark and one to bring up all the saved bookmarks might be good to avoid any sort of accidental presses.

Suggested UI:

I'm sure you can make it look much better but this is kind of what I'm thinking in terms of UI