[ContentReaders] Allocate just the right amount of memory for Lists

Allocate the exact amount of memory for list.
This makes the content loaders more memory efficient and also improves
performance by eliminating the need to perform resizing operations in
the case of big arrays (ex. models with skinnning data).
Merge pull request #2184 from nkast/tnc_ContentReadersLists

[ContentReaders] Allocate just the right amount of memory for Lists