Stack rework and autoclear earmarks feature

Reworked the stack to allow multi-step changes, the new stack functions somewhat differently, instead of two stacks supplementing each other, this version uses a single stack that is iterated through when changes occur and sliced when necessary. The new stack also provides information about what action is currently on the stack to help with moving the focus only when relevant.
The stack rework should allow an easier implementation of #83 further down the line.
Added a new action_completed signal to differentiate cell_changed and earmark_changed from multi-step changes.

The new feature automatically clears related earmarks on insert, I added it as default with a hidden option to toggle it off, it's a feature that new players won't see at all and I think veterans won't pass on, we can promote it later to a full blown option if users want to turn it off.