Implemented a facade for PaymentMethod

[Anindya007]

Noticed there is no PaymentMethod facade implementation in the codebase so I provided one. Please review and merge. Thank you.

[kingIZZZY]

Temporary / hacky workaround:

// add/create
$pm = QuickBooksOnline\API\Facades\FacadeHelper::reflectArrayToObject("PaymentMethod", ['Name' => 'Bitcoin', 'Type' => ['value' => 'NON_CREDIT_CARD']], true );
$pm1 = $dataService->add($pm);

// update - for ex. deactivate (as delete is apparently not supported)
$newObj = FacadeHelper::reflectArrayToObject("PaymentMethod", ['Active' => false], true );
$clonedOfObj = FacadeHelper::cloneObj($pm1);
$pm2 = FacadeHelper::mergeObj($clonedOfObj, $newObj);
$pm3 = $dataService->update($pm2);