add logic for handling copy_from argument

[felixlut]

This PR introduces the copy_from argument when creating a SonarQube Quality Gate.

It does so by calling the api/qualitygates/copy API as opposed to the regular api/qualitygates/create endpoint if the copy_from argument is supplied.

Resolves #131

[felixlut]

Testing the copy functionality is not trivial since it's only really the conditions for it that are copied. This in combination that a Quality Gate is created with a number of conditions by default makes it a bit hard.

My idea right now is to do the following steps:

1. Create a base Quality Gate (including the default conditons that comes with this call)
2. Create a custom condition for it on top of the default ones 
3. Create a copy of the base gate
4. Check that the custom condition is indeed in the list of conditions in the copy

Conceptually this is quite easy, but I'll probably have to dig into custom validation functions a bit to make it work

[felixlut]

Testing the copy functionality is not trivial since it's only really the conditions for it that are copied. This in combination that a Quality Gate is created with a number of conditions by default makes it a bit hard.

My idea right now is to do the following steps:

1. Create a base Quality Gate (including the default conditons that comes with this call)

2. Create a custom condition for it on top of the default ones

3. Create a copy of the base gate

4. Check that the custom condition is indeed in the list of conditions in the copy

Conceptually this is quite easy, but I'll probably have to dig into custom validation functions a bit to make it work

Ended up changing step 4 to checking for equality between the base and copied gates