New puzzle packs

Version 1.60.0 includes three new packs of puzzles, along with some other small improvements. The changes in detail:

• ​There are two new packs of quirky puzzles and a new pack of premium 9x9 puzzles. These special types of puzzle are the hardest to generate using the built-in puzzle generator, so the packs offer a more convenient way to play these sorts of puzzle.
• The difficulty ratings for puzzles in the existing quirky packs and 9x9 pack have been re-assessed and revised in some cases. The aim is to ensure that the difficulty ratings for puzzles in these categories are consistent. The new assessment is based on an evaluation of the logic that is needed to solve the puzzles. The puzzles themselves have not changed, so the revised difficulty ratings only affect the scoring. Some packs have also been re-ordered a little.
• When full dark mode is in operation and a puzzle starts with pre-filled blocks, the blocks can be seen more clearly against the background of the empty puzzle. Pre-filled blocks only occur in 9x9 puzzles generated by the puzzle generator.
• More improvements to the way the difficulty is estimated for new puzzles generated by the puzzle generator.
• A fix for issues with scrolling when switching between puzzle pack categories.
• A fix for the way candidate values are added or removed from a group of squares for the case of when a previous update left the squares with less candidates than number of squares.