Add flower-field, deprecating minesweeper

[BNAndras]

https://forum.exercism.org/t/suggestion-deprecate-minesweeper-for-flower-field/17967/21

Could you label this as rep/tiny?

[glennj]

The minesweeper code can just become the flower code unchanged?

[glennj]

While you're in here, can you add https://stackoverflow.com/questions/tagged/dart to the .lycheeignore file. I thought it was already there, but apparently not.

[BNAndras]

The minesweeper code can just become the flower code unchanged?

The exercise name change is effective immediately for all students. Students who already started Minesweeper may not realize it was changed and now can't find it.

Until a student updates the exercise files, the references to mines will still be in the test suite and instructions. If they update the files, the solution will break since the class name is different so they'd have to go in and fix that as well.

To be frank, I was hoping there would be more of a difference between the two exercises like how beer-song and bottle-song have different test cases. That'd make a clearer case for why Flower Field should be a separate exercise.