Insert new files in SOURCES, HEADERS and FORMS sections in alphabetical order

When adding new files to a project or when renaming files using Qt Creators tools for that, these files are always added to the end of their respective sections. That causes merge conflicts if more than one developer adds files, as they both end up at the bottom of the section. This always requires manual editing to fix, if only to add the now missing \.

It would be beneficial if creator would not insert the files at the end of the section, but just before the first item that is "bigger" sorting-wise. That means that if your list is alphabetically sorted already, it would still be after creator has inserted the file in the project, but it would not re-sort the whole list.

The added benefit would be that for most new classes, only one line per section would be touched instead of two, as no \ would need to be added to the previous line when it is inserted anywhere but as the last item. That makes for cleaner commits.