add leveldb store

1. switch to viper for filer store configuration
2. simplify FindEntry() return values, removing “found”
3. add leveldb store

weed/filer2/filerstore.go

@@ -1,11 +1,16 @@
 package filer2
 
-import "errors"
+import (
+	"errors"
+	"github.com/spf13/viper"
+)
 
 type FilerStore interface {
+	GetName() string
+	Initialize(viper *viper.Viper) (error)
 	InsertEntry(*Entry) (error)
 	UpdateEntry(*Entry) (err error)
-	FindEntry(FullPath) (found bool, entry *Entry, err error)
+	FindEntry(FullPath) (entry *Entry, err error)
 	DeleteEntry(FullPath) (fileEntry *Entry, err error)
 	ListDirectoryEntries(dirPath FullPath, startFileName string, inclusive bool, limit int) ([]*Entry, error)
 }