Meld for OSX binary updated to upstream version

["Youssef A. Abou-Kewik" <youssef adnan gmail com>]

Meld 3.15.3 has been packaged for OS X and is available here https://yousseb.github.io/meld. Since I'm pulling from master, the version number reads 3.15.4, but it's really 3.15.3. 

I will be more careful in the future to pull the exact tags before packaging.

This release fixes a number of issues that we had in the past in the OSX package. Most notably: this release no longer requires an extra wrapper as the built-in wrapper handles args properly. Unfortunately, we still need the built-in wrapper as there is one environment variable that needs to be passed to Python that I can't figure out how to get rid of without modifying the meld startup script. 

Next on my todo: i18n support for the OSX package and code clean up to get more of this fork into upstream meld. 

PS: It would actually make sense to update the wiki to point to the website instead of the old 1.8 release package as we have many 3.x releases that are pretty stable at this point.

Regards,

Youssef