Update Scratch programs in sorting and searching chapter sections

[courtneycb]

The scratch implementation for binary search and linear search should be updated/improved. This can be found in the 'code to run' section here: https://csfieldguide.org.nz/en/chapters/algorithms/searching/#binary-search

Same goes for the scratch implementation of quicksort and selection sort. This can be found in the 'code to run' section here: https://csfieldguide.org.nz/en/chapters/algorithms/sorting/#quicksort

Consider using a variation of: https://scratch.mit.edu/projects/371086023/editor/ (check if we need permission).
Note that quicksort doesn't work because of the way Scratch ignores variables local to one function in recursion.

For more info it would be best to chat with Tim.