ref: embed files, bump to go 1.16 (#167)

* ref: embed portion of files
* fix: readd pkger
* ref: embed version.txt
* fix: wrong mail template import path
* refactor: get rid of sql-migrate
refactor: get rid of pkger in favor of go embed (resolve #164)
* chore: remove unused var [ci-skip]

Co-authored-by: Ferdinand Mütsch <ferdinand@muetsch.io>

migrations/20210411_drop_migrations_table.go

@@ -0,0 +1,26 @@
+package migrations
+
+import (
+	"github.com/emvi/logbuch"
+	"github.com/muety/wakapi/config"
+	"gorm.io/gorm"
+)
+
+func init() {
+	const name = "20210411-drop_migrations_table"
+	f := migrationFunc{
+		name: name,
+		f: func(db *gorm.DB, cfg *config.Config) error {
+			migrator := db.Migrator()
+
+			if !migrator.HasTable("gorp_migrations") {
+				return nil
+			}
+
+			logbuch.Info("dropping table 'gorp_migrations'")
+			return migrator.DropTable("gorp_migrations")
+		},
+	}
+
+	registerPostMigration(f)
+}