Rework db layer.

Add database checker.
Rename SkinsRepositoryInterface and CapesRepositoryInterface methods.

db/fs/fs.go

@@ -0,0 +1,37 @@
+package fs
+
+import (
+	"os"
+	"path"
+	"strings"
+
+	"github.com/elyby/chrly/model"
+)
+
+func New(basePath string) (*Filesystem, error) {
+	return &Filesystem{path: basePath}, nil
+}
+
+type Filesystem struct {
+	path string
+}
+
+func (f *Filesystem) FindCapeByUsername(username string) (*model.Cape, error) {
+	if username == "" {
+		return nil, nil
+	}
+
+	capePath := path.Join(f.path, strings.ToLower(username)+".png")
+	file, err := os.Open(capePath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, nil
+		}
+
+		return nil, err
+	}
+
+	return &model.Cape{
+		File: file,
+	}, nil
+}