remove md5 checksum support

Following up on #2719.  MD5 checksums are
* nowhere mentioned in our docs
* not used in any existing Cask
* deprecated in Homebrew
Therefore it seems sensible to delete this code.
more reliable way to look up username

`ENV` is manipulable.  `getpwuid` is reliable.
Add LibreCAD
Add ZendStudio

Add ZendServer

Update and rename zend-studio.rb to zendstudio.rb

Update and rename zend-server.rb to zendserver.rb
Add DEVONThink Pro 2.7.3

Add cask for DEVONThink Pro 2.7.3
App complains about being installed in `~/Applications/` on first launch but this can be dismissed.
Update Widelands to Build 18
Add (unoffical) Google Music app v1.0.2
Merge pull request #3093 from kevinoconnor7/google-music

Add (unoffical) Google Music app v1.0.2
Merge pull request #3090 from deepj/widelands

Update Widelands to Build 18
add CLI binary for Golly.app
Merge pull request #3076 from rolandwalker/user_from_etc

more reliable way to look up username
Merge pull request #2931 from rolandwalker/remove_md5

remove md5 checksum support
Merge pull request #3091 from rolandwalker/golly_binary

add CLI binary for Golly.app
Merge pull request #3087 from ndr-qef/librecad

Add LibreCAD
Merge pull request #3078 from bingfoon/master

Add Zend Studio 10.6.0
remove OmniOutliner Pro Cask

closes #2777.  This was discontinued as a separate product.
fix broken URL for OmniWeb
the "latest" url contained a versioned subdir
fix broken app link for CLIX.app
fix broken URL for doubletwist.app