Grammar updates to whitepaper.md

Made consistent use of "blockchain" versus "block chain". Arguably, the choice is arbitrary, but this whitepaper should be consistent.  Also removed some instances of capitalization of Blockchain.  There were several uses of "Bitcoin blockchain" where "Bitcoin" was unnecessary to disambiguate.  (Nowhere in this paper is the Factom Chain referred to as a block chain.)

Note there were several uses of Factom as grammatically plural, e.g. "Factom keep" and "Factom also limit" and "How Factom Work".  I considered suggesting what I think was meant to be a plural concept in these contexts such as "Factom Chains"; however, I was not sure enough so I usually just made the verb tense correct.