Improve compatibility with ceres::Solver

1. Default linear solver is Eigen::LDLT
2. Options::max_iterations -> Options::max_num_iterations
3. Options::error_threshold -> Options::cost_threshold
4. Options::relative_step_threshold -> Options::parameter_threshold
5. Options::initial_scale_factor -> Options::initial_trust_region_radius
6. The default values of the above parameters have been changed
   to match those in ceres::Solver::Options
7. Status::RUNNING has been removed
8. Update now returns a bool instead of a Status enum and
   the status handling has been included in the main loop.
9. Summary::gradient_norm has been changed to Summary::gradient_max_norm
   to match the convergence test
10. A member variable cost_ has been added which is computed by Update
11. The test for parameter_tolerance based convergence is made
    more robust near zero.
12. Use of double has been replaced by Scalar.
13. Minor clang-formatting

Change-Id: I3cb0e2fd0a0204476bb8718761dc740cdf5e42ce