Model refactor, part 3 (#4152)

* Remove manager.Repository
* Refactor other repositories
* Fix tests and add database mock
* Add AssertExpectations method
* Refactor routes
* Move default movie image to internal/static and add convenience methods
* Refactor default performer image boxes

internal/api/routes.go

@@ -0,0 +1,15 @@
+package api
+
+import (
+	"net/http"
+
+	"github.com/stashapp/stash/pkg/txn"
+)
+
+type routes struct {
+	txnManager txn.Manager
+}
+
+func (rs routes) withReadTxn(r *http.Request, fn txn.TxnFunc) error {
+	return txn.WithReadTxn(r.Context(), rs.txnManager, fn)
+}