Separate the build task. We will have the following:

This is the same as the previous behaviour:
- UploadStable
- UploadUnstable

This is for creating the zip package only:

- Stable, DoRelease
- Unstable, DoRelease

This is for uploading to S3:

- Stable, Upload
- Unstable, Upload

This is for uploading to nuget:

- Stable, UploadNuget
- Unstable, UploadNuget