Convert .csproj files to portable class libraries
Mary-Jo-Lisa; always the same... (Allow connection strings to be pulled by name from IConfiguration)

This change allows connection strings to be stored in any format supported by IConfiguration and then retrieved using just the name or the "name=" syntax in UseSqlServer and equivalent.

This change doesn't include anything to get IConfiguration registered and it doesn't include a way to get connection strings out of app.config/web.config, although that could potentially be done with an appropriate IConfiguration source.
Fixing build break caused my merge error.
Remove unused references from .csproj files
Target net451 in projects that depend on Microsoft.Data.Common

Resolves #177
Space-age composite polymer; not a shred of sqlmetal... (Support composite keys end-to-end)

This change adds support for value generation with composite keys which was blocking use of composite keys end-to-end. The state entry will now generate values for any property marked to have value generation on add regardless of whether that property is part of a key, composite or not.