Split transcriptions from the elements Vuex module into a Pinia store

To make migrating the elements module to Pinia easier (#1142), 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