Added: Creating project with symlinks

Previously it wasn't possible to create project with symlink.
Now you can set in the preferences of xCodeCapp if you want to create your project with symlink or not with a radioButton.
When launching xCodeCapp, the system will check if $CAPP_BUILD is defined or not. If not, the button in the preference will be disabled and a toolTip will advice how to create a $CAPP_BUILD variable.