✨ Updated theme activation API to experimental
✨ Updated theme activation API to experimental

- allow both uploading and activating themes as experiemental API features
- previously only uploading was allowed, I believe purely due to an oversight

Kikobeats/Ghost,TryGhost/Ghost,ErisDS/Ghost,TryGhost/Ghost,JohnONolan/Ghost,kevinansfield/Ghost,ErisDS/Ghost,kevinansfield/Ghost,JohnONolan/Ghost,bitjson/Ghost,janvt/Ghost,Kikobeats/Ghost,janvt/Ghost,kevinansfield/Ghost,JohnONolan/Ghost,Kikobeats/Ghost,e10/Ghost,TryGhost/Ghost,e10/Ghost,bitjson/Ghost,ErisDS/Ghost