#107 Enable keeping newer files on "reuse existing project"

[Stefan Rossbach]

From the saros survey
"While accepting an invitation, make somewhat like 'Retain the latest verions of the files' so that if I am invited and one of my files is newer than the one of my buddy, my file is not overwritten, but his is. That would work for most cases like that when people mostly separate the areas of the project where they work in file-specific fashion."

Add the possibility to configure saros, so that newer files (sync clocks first) are kept on the invited users side, and sent back the host.