* 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
