First stab at content packages

- Added "content" projects to be able to at least release something that
is tested and have a home for these files.
Imagine this being gangnam style

- Made it compile
- Made tests work
- Says nothing right?
- Moved the IAggregateRootEntity and Entity impl to the various content
projects
Pack your bags and leave

- Packing all content and making it push-worthy
Sexy lady - Whop Whop

- Serious self inflicted spanking ... when you copy paste!
Merged with master
NET40 wants more

- Content projects now get a NET40 counterpart
- Excluded the async bits from NET40 for now
- Integrated into the build process.
Adjusted release notes