Be able to make a charge with Internet Banking payment method

[guzzilar]

⚠️ This PR is a sub PR of #62

1. Objective

Continue from PR #64.
To be able to make a charge with the Internet Banking payment solution.

Related information:
Related issue(s): 🙅

2. Description of change

• Fix bank icon stylesheet.
  

• Update the Internet Banking checkout form, to have real implementation with the real values.

• Javascript, update the Internet Banking payment object, by observing radio buttons at the Internet Banking checkout form.

• Add a new payment_method_assign_data_omise_offsite_internetbanking event and observer class to observe the parameter that frontend submit through the checkout form.

• etc/DI.XML, update real dependencies (classes that work with OmiseOffsiteInternetbankingAdapter), see OmiseOffsiteInternetbankingCommandPool (virtual object).

• Implement Gateway\RequestBuilder, Gateway\Client, Gateway\Validator classes that need to handle build request object >> request to gateway service >> handle & validate the result steps.

3. Quality assurance

🔧 Environments:

• Platform version: Magento CE 2.1.5.
• PHP version: 7.0.16.

✏️ Details:

1. ✅ Test be able to checkout with the Internet Banking payment method.

   1. Enable the Internet Banking payment solution at the admin payment setting page.

   2. Do normal checkout process, and choose one of bank from the bank list.

   

   3. Then, charge will be completed and redirect buyer to the succesful page. (here, this PR will not validate the payment result).

   4. Check at Omise dashboard, you will see the transaction that made by above step.
      
      

   5. Back to Magento's admin order list page, you will see the last transaction was made with payment Internet Banking payment method.
      

4. Impact of the change

You may need to clear cache if you can't see the result.

1. At Magento admin page, go to SYSTEM > Cache Management
2. Click Flush Magento Cache. (or you can choose to disable all caches while testing).
   

5. Priority of change

Normal

6. Additional Notes

• This PR is a sub PR of Introduce Internet Banking feature to Magento CE 2.x ✨ #62. In order to see the full implementation, please check from that PR.
• This implementation is just focusing on checkout an order with Internet Banking feature, without concerning of a payment result. To prove that the plugin can request to Omise API with the proper parameters and Magento's order can show the name of the payment at an order detail page.

[guzzilar]

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