Migrate missing features and fixes from old SDK

**Topic for discussion**

It is pity that we hit same [issues](https://github.com/commercetools/nodejs/pull/590) with new SDK which has been addressed in [old SDK](https://github.com/sphereio/sphere-node-sdk/blob/master/src/coffee/sync/product-sync.coffee#L44-L56) already as for existing customers migration might be a costly enterprise as they might hit issues that were not present with old SDK. The reason is obviously that rewrite of new SDK was based on old SDK and as it took around 1 year of development all the fixes/features applied to old SDK during that time were not migrated to the new SDK release.

**Suggestion**

Review all issues/PRs/commits from old SDK implemented after rewrite fork and create a list of TODOs for migration like examples below.

**Missing fixes/features**
- [ ] - Sync actions should first [remove variants](https://github.com/sphereio/sphere-node-sdk/blob/master/src/coffee/sync/product-sync.coffee#L45)
- [ ] - fetch all [convenience function](https://github.com/sphereio/sphere-node-sdk/blob/master/src/coffee/services/base.coffee#L227) for multi-paged results
- [ ] - GraphQL convenience method which allows to do GraphQL requests with single line instead of boiler plate utils in every project
- [ ] - Provide GraphQL process function for paginated results and fetch all if one needs to load all paginated results into memory.