Allow to put limited wiki content in save comments

It's currently only possible to put text content in save comments. This is rather limited and prevents for more usecases:

• being able to link for other pages on history comments
• being able to mention people in history comments
• being able to use some inline formatting (bold / strike)
  etc

Right now my main UC is the capability to create a link when merging a Change request from https://extensions.xwiki.org/xwiki/bin/view/Extension/Application%20Change%20Request%20-%20UI/