Added loadBase64Data feature

[jack-szeto]

I added the loadBase64Data feature. So now, it's not limited to save the data to local file system.
You could save the data from getBase64Data and save it somewhere else like database.
Then, load the data using loadBase64Data.

Example

try {
    await controller.loadBase64Data(base64Data);
    // handle success
} catch (e) {
    // handle error
}

[mym0404]

Thanks I'll merge it soon