The collections manager now stores a reverse look-up from the objects within its collections, to the collections that contain that object. This avoids the GetCollectionsContainingObject and GetCollectionsContainingObjects functions having to iterate the collections for each object queried, which can be a large win for large sets of objects.
This also adds some functions needed for the quick asset management feature.
[CL 2570748 by Jamie Dale in Main branch]
UETOOL-332 - Collections 2.0
Removed some duplicated data from FCollection (AssetList and AssetSet) as they had to be manually kept in sync. Only AssetSet exists now, and is converted into an array and sorted before being written to disk (to keep the order consistent for diffing). DiskAssetList has also been converted into a set (now DiskAssetSet) as this is only ever used for lookup queries.
All manually memory management has been removed from FCollectionManager, and the array of maps to collections has been converted into a single map using FCollectionNameType as its key. This simplifies collection lookup code in most cases, and removes the need to manually track the total number of collections outside of the map (NumCollections has now been removed).
Renamed ICollectionManager::GetCollectionsContainingAsset to ICollectionManager::GetCollectionsContainingObject as the function checks for any objects, not just assets.
Renamed FCollection::IsAssetInCollection to FCollection::IsObjectInCollection as the function checks for any objects, not just assets.
Made ICollectionManager::IsCollectionEmpty const.
Replaced all appropriate loop usage with range-based-for, and replaced any NULL with nullptr.
[CL 2560621 by Jamie Dale in Main branch]
