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_add_imprint_content.go

@@ -0,0 +1,47 @@
+package migrations
+
+import (
+	"github.com/emvi/logbuch"
+	"github.com/muety/wakapi/config"
+	"github.com/muety/wakapi/models"
+	"gorm.io/gorm"
+	"gorm.io/gorm/clause"
+)
+
+func init() {
+	const name = "20210411-add_imprint_content"
+	f := migrationFunc{
+		name: name,
+		f: func(db *gorm.DB, cfg *config.Config) error {
+			condition := "key = ?"
+			if cfg.Db.Dialect == config.SQLDialectMysql {
+				condition = "`key` = ?"
+			}
+			lookupResult := db.Where(condition, name).First(&models.KeyStringValue{})
+			if lookupResult.Error == nil && lookupResult.RowsAffected > 0 {
+				logbuch.Info("no need to migrate '%s'", name)
+				return nil
+			}
+
+			imprintKv := &models.KeyStringValue{Key: "imprint", Value: "no content here"}
+			if err := db.
+				Clauses(clause.OnConflict{UpdateAll: false, DoNothing: true}).
+				Where(condition, imprintKv.Key).
+				Assign(imprintKv).
+				Create(imprintKv).Error; err != nil {
+				return err
+			}
+
+			if err := db.Create(&models.KeyStringValue{
+				Key:   name,
+				Value: "done",
+			}).Error; err != nil {
+				return err
+			}
+
+			return nil
+		},
+	}
+
+	registerPostMigration(f)
+}