add Algorithm class
logging as Callback
add Logger class
add extrapolation in forwardbackward
automatic extrapolation in fwbw + example
change algorithms import scheme, add forward_backward wrapper
TODO
add FISTA
fix DataTermGradient.backward
 - correctly pass shape to scipy.linalg.LinearOperator constructor
new algorithm (ADMM) added
added quick computation of backward for dense dataterms
remove unneeded functions and imports from admm
add CallbackMeta for initparam registry
Merge branch 'algorithmclass' of https://github.com/tneumann/convexopt into algorithmclass
pass algorithm to Callback and Logger
add nonnegative l1 norm
add APGM
add IdentityOperator, fix shape of ScaledOperator