docker support with .NET Core 3.0

[bravecobra]

I've made this PR based on #367 by @ChrisSzabo. The amount of work to get it all working properly seemed to be more extensive given the branch was getting rather old. I merged in the latest dev branch, containing the latest .NET Core 3.0 support (#390 ) and the Audit logging (#391 )

So what's changed?

• Fixed the IdentityServerBaseUrl for Swagger API as mentioned in docker support #367
• Fixed Swagger redirect URI misconfiguration
• Fixed the outstanding merge conflicts of docker support #367
• Merged the latest dev branch
• Changed the environment variable to use double underscore. It worked in VS2017 with colons, but VS2019 seems to require it in order to debug properly. docs and SO
• Added a docker-compose.vs.debug.yml and docker-compose.vs.debug.yml to enable debugging with a seeded environment.

We'll need to update the docs, but I suggest getting this in first.

So now we have the following possibility to get a running seeded and debug-able (in VS) environment:

docker-compose build
docker-compose up -d

This PR closes #121

[skoruba]

Amazing work @bravecobra - thanks a lot 😊 I will test it ASAP 👍

[bravecobra]

Don't forget that this still assumes you have the proper migrations generated in place. We can fix that later in the build pipeline I've prepared with github actions. One step at the time...

[xmichaelx]

Looks solid - i've checked the changes in file. Later today I'll download, build and test it on Ubuntu but I think that we want to merge it ASAP.

[xmichaelx]

Looks ok, let's merge it @skoruba