🧠🌴 Remove dependency from braintree-web CDN

[josemigallas]

What this PR does / why we need it:

Remove dependency from braintree-web sdk loaded via CDN by moving the script into a TS file handled by webpack.

Additionally there are some minor improvements, namely:

• Disable the submit button once click to avoid multiple form submissions.
• Move css to a scss file (some typos have been spotted).
• Move hosted fields styles and options to a separate utils file, which will be reused by same form in dev portal.
• Show potential errors in console to help future debugging.

Possible scenarios:

• Scenarios 1: hosted fields failure
  

• Scenario 2: wrong client token

• Scenario 3: wrong credit card

• Scenario 4: braintree error after submission

Which issue(s) this PR fixes

THREESCALE-9152: Remove double dependency from braintree-web SDK

Verification steps

You can verify it still works by going to Account Settings > Billing > Payment Details > edit
(AKA /p/admin/account/braintree_blue/edit)

Then use any of the Braintree test credit cards, such as: 4000000000001000 with any valid exp. date and CVV.

NOTE: you will need to have your gateway configured in master (see test credentials in Bitwarden).

[jlledom]

I tried locally and seems to work fine