Missing projects and their references

This repo has two missing project references i.e
```
 <ProjectReference Include="..\..\..\LTI\LtiAdvantage\src\LtiAdvantage.IdentityServer4\LtiAdvantage.IdentityServer4.csproj" />
 <ProjectReference Include="..\..\..\LTI\LtiAdvantage\src\LtiAdvantage\LtiAdvantage.csproj" />
```
Please add missing projects and references so that we can move further for a sample idea of LTI Advantage Library.