Improvements to soft error mechanism

[Etua]

Currently there are only two categories of "soft" errors which can be discovered in processing individual files that do not affect processing other files. One of them is expected during standard usage (skipping of fpcalc for unsupported files) whereas the other may be a result of no Internet connection which for now will result in skipping every step after downloading JSON leaving target directory empty.

Right now their only indicators are printed messages for CLI mode. I think that some type for listing errors should be defined with typedef so even success messages would contain complete information like "X files moved. Y files skipped because of unsuitable type. Z files skipped because of network errors." That way it would be easier to add other error types in the future.