* 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
* Allow disabling notifications per user and disabling specific notifications per use
closes#1974
* Add disable notifs for all users
* fix term generator for notifications
* sow checkboxes instead of multiselect when js is enabled
* remove js dependency
* fix notif conditions
* init u2f
* ux fixes
* Cleanup Manage Controller
* final changes
* remove logs
* remove console log
* fix text for u2f
* Use Is Secure instead of IsHttps
* add some basic u2f tests
* move loaders to before title
* missing commit
* refactor after nicolas wtf moment
