* 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
* This refactors the email sending so that all the logic related to users and emails are now contained in one location.
* The Reset password screen has been updated from its ugly plain self to use the same layout as the login.
* An admin can now create a new account without specifying a password. A link is generated that can be given to the intended user to configure the password. If emails are configured, it also sends an email
* An admin can now create accounts that still require the user to verify their if the setting is enabled from the server settings. A link is generated that can be given to the intended user to configure the password. If emails are configured, it also sends an email.
* The above features can be used in conjunction: An email will have to verify their email through a link. Once verified, the user is redirected to setting the password.
* When an email has been verified OR a password has been set, users are now redirected to the login page with the email filled in and a success status message shown instead of a dedicated thank you page.
This adds a "Custom Theme CSS file" to the "Server settings: Theme" page. It works similar to the custom bootstrap and creative start fields, but is only added to the head in case it is set.
The main idea here is that users would choose one of our predefined themes and have the option to override specific values. The other apporach would be to let the custom theme replace the predefined one, but this could lead to issues in case we extend the set of variables, which would be unset then.
This way users can copy a predefined theme and override all variables or just the ones they want to customize.
The help icon besides the label links to a page in the docs I'm currently working on.
