Make possible to build tasks separately and use the cached build output in further needs

The build process output should be possible to re-use, so that we don't need to build tasks again if we want to upload them to S3 cloud, or in order to generate Moodle exam. 

Basically, we keep the currently used temporal directory with a parameter and then pass the directory for `upload` or `moodle` arguments so that we can use the old files without re-generation.