Database update

- Removed read-only mode
- Added LevelDB for big data storage

TODO: Update backup utilities to support new db structure

src/mod/database/dbinc/dbinc.go

@@ -0,0 +1,39 @@
+package dbinc
+
+/*
+	dbinc is the interface for all database backend
+*/
+type BackendType int
+
+const (
+	BackendBoltDB  BackendType = iota //Default backend
+	BackendFSOnly                     //OpenWRT or RISCV backend
+	BackendLevelDB                    //LevelDB backend
+
+	BackEndAuto = BackendBoltDB
+)
+
+type Backend interface {
+	NewTable(tableName string) error
+	TableExists(tableName string) bool
+	DropTable(tableName string) error
+	Write(tableName string, key string, value interface{}) error
+	Read(tableName string, key string, assignee interface{}) error
+	KeyExists(tableName string, key string) bool
+	Delete(tableName string, key string) error
+	ListTable(tableName string) ([][][]byte, error)
+	Close()
+}
+
+func (b BackendType) String() string {
+	switch b {
+	case BackendBoltDB:
+		return "BoltDB"
+	case BackendFSOnly:
+		return "File System Emulated Key-Value Store"
+	case BackendLevelDB:
+		return "LevelDB"
+	default:
+		return "Unknown"
+	}
+}