Plotextractor

- Properly supports cases where images are located in
a nested folder inside the extracted tarballs root folder.

- Adds wrapfigure support.
- Catches problems with image conversions.
- More robust handling of image rotations in TeX sources.
- Removes unicode_literals usage.

- Improves extraction from TeX file by reading files with encoding.

- Initial export from Invenio Software <https://github.com/inveniosoftware/invenio>
- Restructured into stripped down, standalone version