Remove levels, along with removing/replacing covers

I_am_Zero

As people progress from 1* to 2* to 3* teams, they use the lower tiered teams less and less. Rather than selling off the character completely, allow us to lower the levels while also gaining some ISO back, say half the cost of the level. So, if it cost 500 ISO to level a character from 25 to 26, then if you lower the level from 26 to 25, you get back 250 ISO. This will allow you to keep the character if you want to use it later on down the road, and make use of the ISO you used to build that character for another character.

This goes along with allowing us to remove/replace covers. Some characters, Iron Man 40 in particular, have optimal builds that don't max out the power level. If I have a 5/5/3 IM 40 and want to go down to 5/5/2, being able to sell off a cover would be nice. This goes along with removing levels on the character. If you sell a cover and you have levels that are higher than you would normally have, it would sell those levels back to you for half the ISO points.