(Internal) Namespace for Tours

Currently, the system whines if you try to create a tour with a name that already exists. Might work for small-scale instances, but will get annoying super fast on larger servers. Tried to create a "Test" tour, which failed as I suppose one of you already has a test tour.

Possible solutions:

• Internally prefix tours with the owners name and dont show it publicly.
• Accept that a name is just a label and make it per user. store it an a map like tour.name[username]="Test" and on sharing check if "Test" already exist, if yes append like tour.name["InvitedUser"]="Test"+checkForNextAvailableNumber("InvitedUser","Test").
• Prefix/Suffix tours, but only on shared tours and make tour names unique per user. Aka I'm allowed to have "Test", if I share it with Lars, Lars has it shown as "Test shared by Matthias". I tend to see the latter as most elegant, but I'm open for suggestions.

Assign labels, Milestones and so on as you see fit @larsmeiendresch