Adds cursors db operation interface

[jorgeantonio21]

The interface follows:

pub trait CursorLoader {
    fn get_cursor(&mut self, output_module_hash: String) -> Result<Cursor, DBError>;
    fn update_cursor_query(
        &mut self,
        module_hash: String,
        cursor: Cursor,
    ) -> Result<usize, DBError>;
    fn write_cursor(&mut self, module_hash: String, cursor: Cursor) -> Result<usize, DBError>;
}