Delete all unused assets

[TriNityGER]

@Pierdek;637397

UE4 has WrangleContentCommandlet which should remove all unused assets, it is undocumented feature and may not work very well.
It can be launched this way:

UE4Editor.exe "Myproject\MyProject.uproject" -run=WrangleContent -allmaps

It may take some additional parameters to setup it’s behavior:

// overall commandlet control options
bool bShouldRestoreFromPreviousRun = FParse::Param(*Params, TEXT("restore"));
bool bShouldSavePackages = !FParse::Param(*Params, TEXT("nosave"));
bool bShouldSaveUnreferencedContent = !FParse::Param(*Params, TEXT("nosaveunreferenced"));
bool bShouldDumpUnreferencedContent = FParse::Param(*Params, TEXT("reportunreferenced"));
bool bShouldCleanOldDirectories = !FParse::Param(*Params, TEXT("noclean"));
bool bShouldSkipMissingClasses = FParse::Param(*Params, TEXT("skipMissingClasses"));

// what per-object stripping to perform
bool bShouldStripLargeEditorData = FParse::Param(*Params, TEXT("striplargeeditordata"));
bool bShouldStripMips = FParse::Param(*Params, TEXT("stripmips"));

// package loading options
bool bShouldLoadAllMaps = FParse::Param(*Params, TEXT("allmaps"));

// if no platforms specified, keep them all
UE_LOG(LogContentCommandlet, Warning, TEXT("Keeping platform-specific data for ALL platforms"));

FString SectionStr;
FParse::Value( *Params, TEXT( "SECTION=" ), SectionStr );

Whenever I tried this command, it never did anything.