Merge conflict feedback

[brunopostle]

ifcmerge will return 0 on success, otherwise it will report unresolvable conflicts in some detail. Sometimes these conflicts will be resolvable by committing some changes and trying again, but other times it won't be possible.

This feedback from ifcmerge needs to be presented in the GUI in some useful fashion.

In addition a merge conflict could be the result of attempting to merge multiple branches in the wrong order (because confict resolution is necessarily asymmetrical), the only solution to this would be some helper that tried merging branches in all possible combinations to find the best option.