Add winmerge to rapps

Winmerge compare files/folders under windows, work fine in reactos now, i testing the 2.14.0 version (portable), in this post (in the forum) can see a screenshot https://www.reactos.org/forum/viewtopic.php?f=2&t=10972&start=720
The official web site is http://winmerge.org/ and the license is GPL, thanks.