* added _safeTransferFrom function

* added safeMint functions

* added package-lock.json for consistency, don't know why it changes

* added initial suggestions/modifications

* change _safeTransferFrom to internal, reverted package-lock.json to original, and changed ERC721Pausable to override _transferFrom instead of transferFrom

* included tests for safeMint functions

* modified safeMint tests to be on ERC721Mock contract

* added safeMint to ERC721Mintable & respective test to ERC721MintBurn.behavior.js