Bump version to v424
Calc MD5 in setters for sound and costume data
Merge pull request #486 from LLK/recalculate-md5-b

Calc MD5 in setters for sound and costume data
Setters null the MD5 instead of calculating it

Calculating the MD5 on every change was proving to be a performance
problem for some larger assets
Merge pull request #487 from LLK/v424

v424