Fix rst files for inversion docs

Moved filenames around so that docs build for the inversion package
Finished MultiObjective

Was missing all the docstrings.
Missing division import in solvers and base

Forgot the from __future__ import division line and would get errors due
to integer division.
Module inversion.misfit with data-misfit funcs

For now there is only the L2Norm data-misfit function. This is what is
subclasses when implementing new inverse problems.
Converted geothermal.climsig to new framework

Unified the inversion inside a single class that takes a mode argument
to distinguish between linear and abrupt changes