Split transcriptions from the elements Vuex module into a Pinia store

To make migrating the elements module to Pinia easier (#1142 (closed)), and then get more maintainable Pinia stores, we need to split it into multiple stores. The elements module does not need to handle transcriptions. We can move those to a new transcription Pinia store.

This means moving the following:

• The transcriptions state
• The setTranscriptions mutation
• The removeTranscription mutation
• The createTranscription action
• The updateTranscription action
• The deleteTranscription action
• The listTranscriptions action