Feature/5.6/tup 1785 remove workspace from connection

Please @ggu-talend could you review those changes, test them and merge it if they are ok.
1) I have removed the notion of workspace from the Connection classes, removed it from the GUI too although now you have the workspace info at the bottom of the connection not to confuse our existing users too much.
2) I have created a workspace dialog prompt that pops up when launching on the same workspace or if the user check the preference Startup and Shutdown->Workspaces/Promp for workspace on startup. And also added a new menu item File/switch workspace identical to the eclipse one.
3) I have added a system property to force the prompt on the first launch if we want (Mike was not sure)
4) I have moved the connection file from the /configuration folder to the workspace folder