An update of the wizard for adding properties to SD-files

These commits make the following changes:
* Make the wizard decide what sign that is used for separating the values by looking in the file instead of depending on the file-extension.
* It can now handle values separated with blank-spaces and semicolon as well as tab and comma.
* It can now handle a file with a "missing" top left element, e.g. a file where the data has both row- and column-header.
* Make the items in the combo box menu work properly.
* Updates the help-page (images and the description of the data-file format).
* Adds an example to the help page.

If someone thinks that this changes might be better of in the 2.6.1 branch, then tell me and I'll send the pull request to that instead.