Add the possibility to execute an action implemented in CRM using the API

[AllanDeCastro]

Currently, we can create, update, delete and retrieve records but it is impossible for us to execute an action implemented in CRM.

It would be great to be able to call this: this._context.webAPI.execute(request).then(successCallback, errorCallback); as mentionned in the Dynamics docs: https://docs.microsoft.com/fr-fr/dynamics365/customer-engagement/developer/clientapi/reference/xrm-...

Thank you for all the work already done!