Make it possible to step backwards

[SzNagyMisu]

Or simply jump to any previous steps.

Issues that might arise with this

• changing the table size when there's already content in it
• adding a black cell where there is number / solution highlight / letter already
  • most importantly, if there's number, the program will need to recalculate all the numbers

[SzNagyMisu]

Steps of implementation

• introducing maxStepReached: number state variable
  • steps in step indicator are clickable if their index is smaller than or equal to maxStepReached
  • clicking "Next" would increment maxStepReached if the current step was the max
• pulling together steps that don't need to be separate
  • define black and solution cells (add radio switch to decide which)
  • add letters and definitions (possibility to hide definitions)
  • consider renaming the components (AddNumbers.vue too)
• when modifying table size, check if there's actual value in a cell before assigning empty value to it
  • if there are definitions already they might stay (it's an edge case I don't want to cover)
  • might need to double check if it breaks the definition words
• when black cells are added set cell to {isBlack: true} to remove any letter / number / arrow / solution background

[SzNagyMisu]

Done. Instead of pulling together black + solution cells and letters + definitions, I rather separated numbers + turns. Also, resizing a crossword table with definitions already existing for a part we want to cut out will result in an error but that's not an expected / supported flow anyway.