ch4 fixes
ch4 flow and comment fixes
content fixes, clarifications, new diagrams, flow fix
re-arranged private key content and started on wallets
Merge branch 'chapter/Chapter4' into develop

* chapter/Chapter4:
  re-arranged private key content and started on wallets
  content fixes, clarifications, new diagrams, flow fix
  ch4 flow and comment fixes
  ch4 fixes

Conflicts:
	ch04.asciidoc