Release 0.4.0

• fix/clean-up #177
• Feature/community fee collector #176
• Fix/exchange-setup-assertion #173
• Remove naming of new Datatokens internally. Name and symbol now has t… #175
• add FixedPrice helpers #172
• Feature/ocean fee #167
• Fix publishing artifacts to pypi package #169
• feature/rename-spool-sfactory #170
• Feature/update fixed rate exchange docs #166
• Feature/update ddo docs #165
• Feature/DDOOwnershipTransfer #164
• On-chain history #136
• Release/v0.3.5 #159
• update DDO events parameters #158
• prepare docs for release v0.4 3889a86
• Rename SPool to BPool 39b9400
• remove converter dfe2bae