ENH: add infimal convolution as an abstract functional (#1075)
ENH: add infimal convolution as an abstract functional (#1075)

* add infimal convolution as an abstract functional
* make changes based on review. Mainly style changes.

kohr-h/odl,kohr-h/odl,odlgroup/odl,aringh/odl,aringh/odl,odlgroup/odl