Add cocktail v7.6.1 (Mavericks edition) cask and remove SHA checks on all Cocktail casks

See also pull request in main repository: [Update cocktail to 8.0 (Yosemite edition)](https://github.com/caskroom/homebrew-cask/pull/6849)

Moved old Mavericks edition (v7.6.1) cask to this repository: `cocktail-mavericks`

Removed SHA checks from cocktail casks because vendor downloads are unversioned.