Consistently use technical name of themes to identify them

[shyim]

Description

In most places themes are identified by their technical name. The only place where the id is used is during the generation of the hash value for the asset folder. It would be much easier to generate the same folder structure between different systems if the technical name would be used there as well.
Example

We tried to pre-generate the css/js files during deployment jobs which was not really possible due to this.