add io submodule for import scenes

[edgarriba]

The first of a set of functions in order import scenes from different structure from motion frameworks such Bundler, VisualSfM, OpenSfM, OpenMVG and TheiSfM.

The current PR has a Bundler import function, a sample code with its correspondent tutorial

[alalek]

Looks good!
Could your please squash commits into one to eliminate unnecessary intermediate changes (picture added in both commits)

[alalek]

Something is going wrong during commits squash. Another commit with "CompilerFix" has been added and merged here: #484 (a5e7d8f)

$ git fetch upstream
$ git rebase -i upstream/master
# Edit to this and save:
# pick 0726948 add io submodule for import scenes
# f 698bfb7 fix rotation issue + small docs errors
$ git push -f origin sfm

Or use something like this #290 (comment)

[alalek]

Thank you!
👍

[alalek]

@edgarriba Please remove your opencv_extra:sfm branch

[edgarriba]

done