Provide ManageForms option on API 3 Active Campaign wrapper

Problem/Motivation

The TestMonitor ActiveCampaign API 3 wrapper does not provide all the fuctionality the module needs, so it needs to be added first.

The ability to retrieve forms must be present, otherwise the embed capability, the custom field and the webformhandler would no longer be usable.

Steps to reproduce

Proposed resolution

Add the needed class, functions and make a pull request on the github of the wrapper.

Remaining tasks

User interface changes

API changes

Active Campaing API V1 to API V3

Data model changes