Context back() and canBack() implementation

[devnatan]

This feature was available in v2 as experimental but was removed in v3+ and is now back.

Possible usage will be documeneted on Wiki
History is controlled by context's open* and close*. Do not support Shared Contexts for now.

Closes #277
Fixes #461
Fixes #451

onResume(...) calls will be implemented later.

canBack can be combined with displayIf to create a "go back" item

firstSlot(new ItemStack(Material.ARROW))
    .displayIf(Context::canBack)
    .onClick(Context::back);

Navigating Between Views docs should be rewritten before v3.0.0-rc.3

[luiz-otavio]

👍