Is it possible to make space for a double-pole breaker in this panel?
Ah, the tricky GE Qline.  


Convert the dishwasher to a 1-pole double-stuff breaker set low in the space. 
Pop off the cover above it.  Now you have 1 space but it's a half space off-beat. 
Get a unique Qline double-stuff 2-pole 30A breaker, that is 1" wide and made to go in off -beat spaces.  (And they require the off-beat, they can only work there). 
Move the water heater to that breaker.
Voila, 2 full spaces freed. Use that for your 90.