* More Options refactoring
Continues refactoring config classes to use the propert Options pattern where possible.
DataDirectories and DatabaseOptions are now configured the Options pattern and the BTCPayOptions is now moved alongside the other config setup
* Move COnfigure logic for Options to the Startup
This allows plugins to create custom dbcontexts, which would be namespaced in the scheme with a prefix. Migrations are supported too and the table would be prefixed too
* BTCPay Extensions Part 2
This PR cleans up the extension system a bit in that:
* It renames the test extension to a more uniform name
* Allows yo uto have system extensions, which are extensions but bundled by default with the release (and cannot be removed)
* Adds a tool to help you generate an extension package from a csproj
* Refactors the UI extension points to a view component
* Moves some more interfaces to the Abstractions csproj
* Rename to plugins
