Add GraphQL interface

[mvantellingen]

Note that this is a work in progress (missing unittest)

Example usage:

var respData struct {
	Product struct {
		ID      string `json:"id"`
		Version int    `json:"version"`
	} `json:"product"`
}

query := client.NewGraphQLQuery(`
	query ($sku: String!)  {
		product(sku: $sku) {
			id
			version
		}
	}
	`)
query.Bind("sku", "mysku")

err := query.Execute(&respData)
if err != nil {
	panic(err)
}
fmt.Println(respData.Product.ID)

See also https://github.com/labd/terraform-provider-commercetools/pull/109/files

[davidweterings]

Looks pretty clear to me 👍

[codecov]

Codecov Report

Merging #49 into master will increase coverage by 0.05%.
The diff coverage is 26.38%.

@@            Coverage Diff             @@
##           master      #49      +/-   ##
==========================================
+ Coverage   10.57%   10.63%   +0.05%     
==========================================
  Files          61       62       +1     
  Lines       13160    13227      +67     
==========================================
+ Hits         1392     1407      +15     
- Misses      11612    11661      +49     
- Partials      156      159       +3     

Impacted Files	Coverage Δ
commercetools/client_graphql.go	0.00% <0.00%> (ø)
commercetools/client.go	68.78% <63.33%> (-1.49%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 8c16178...fb8e54c. Read the comment docs.

[mvantellingen]

Need to add unittest later (want to get a poc working for custom apps first)