Some changes in SRBA library

- Added an output variable for the optimization results yielded by stage
1 when optimizing edges.
- Added a variable to contain the observation RMSE error after
optimization.
- Support for independent selection of robust kernel in both stages when
optimizing edges.
Start of example to test obs removal
Fixed potential error in new keyframe pose initialization
Merge branch 'experimental-srba-branch' of https://github.com/jlblancoc/mrpt into experimental-srba-branch
srba: log initial/final relative poses for verbosity>=2
Merge pull request #77 from jlblancoc/experimental-srba-branch

Experimental srba branch