Formatting solitaire.h

Commented out some logging in algorithms/deep_cfr.py

Fixed bug where legal actions weren't sorted

Solitaire changes for Colab

Remove an #include <optional> to help with https://github.com/deepmind/open_spiel/issues/436

Use absl::string_view instead of std::string_view. Ongoing fixes for https://github.com/deepmind/open_spiel/issues/436

Remove instances of std::optional as it causes compliance problems in some environments (use only absl::optional)

Skip games not loadable.

Merge pull request #429 from michalsustr:sim_move_games

Merge pull request #430 from janrvdolf:fix-loading-matrix-as-efg

Fixes the path in regenerate_playthroughs.sh.

Updates integration_tests/playthroughs for matrix_rps.

Adds implementation of the UtilitySum method into the NormalFormGame class.

Removes computation of utility sum from 'matrix_game.h'.

Adds override specification for UtilitySum method in matrix games.