V2 alpha - initial version (#172)

Initial alpha codebase for version 2 of WireGuard Portal.
This version is considered unstable and incomplete (for example, no public REST API)! 
Use with care!


Fixes/Implements the following issues:
 - OAuth support #154, #1 
 - New Web UI with internationalisation support #98, #107, #89, #62
 - Postgres Support #49 
 - Improved Email handling #47, #119 
 - DNS Search Domain support #46 
 - Bugfixes #94, #48 

---------

Co-authored-by: Fabian Wechselberger <wechselbergerf@hotmail.com>

internal/domain/mail.go

@@ -0,0 +1,18 @@
+package domain
+
+import "io"
+
+type MailOptions struct {
+	ReplyTo     string // defaults to the sender
+	HtmlBody    string // if html body is empty, a text-only email will be sent
+	Cc          []string
+	Bcc         []string
+	Attachments []MailAttachment
+}
+
+type MailAttachment struct {
+	Name        string
+	ContentType string
+	Data        io.Reader
+	Embedded    bool
+}