Runtime enviroment (skip SSL on localhost)

[marcelino-borges]

Changes made to the feature:

• Added the possibility of bypassing SSL verification when the developer is running the app in localhost;
• Patch on MercadoPagoConfig class, adding the field runtime_enviroment and class constants for LOCAL and SERVER options, as well as getter and setter for the runtime_enviroment;
• Patch on MPDefaultHttpClient class, adding logic to the function createHttpRequestOptions that will allow the program to check if the dev has configured runtime enviroment to LOCAL, setting to false both CURLOPT_SSL_VERIFYHOST and CURLOPT_SSL_VERIFYPEER in options array in case he's set to LOCAL;
• Created a InvalidArgumentException class (used in MercadoPagoConfig->setRuntimeEnviroment()).

General changes

• Added documented flows in README.md about Checkout Pro (Preferences creation)

Issues closed

• Closes #486

OBS

• Unit tests not added considering there were no tests implemented for these existing classes

PR validation checklist:

• Title and clear description of the PR
• Tests of my functionality
• Documentation of my functionality
• Tests executed and passed
• Branch Coverage >= 80%

[rhames07]

PR Reviewed! Thank you for your contribution @marcelino-borges !