Fix license in package.xml or file headers

[shr-project]

Can you please fix the license version in package.xml?

Currently
https://github.com/ros-perception/slam_karto/blob/melodic-devel/package.xml#L12
says only LGPL, while:
https://github.com/ros-perception/slam_karto/blob/melodic-devel/src/slam_karto.cpp#L5
says CCPL (looks like some CC-BY-* variant)
https://github.com/ros-perception/slam_karto/blob/melodic-devel/src/spa_solver.cpp#L5
says LGPL-3+

superflore maps this to LGPL-2 in:
https://github.com/ros-infrastructure/superflore/blob/master/superflore/utils.py#L179
and LGPL-2 isn't valid SPDX Identifier in:
https://spdx.org/licenses/
so it would be better to declare the license correctly at the source - in package.xml.

[mikeferguson]

I'm actually not exactly sure what "single" license we could put there. This package pulls the SPA solver code from the Karto release (so the LGPL-3+ is correct there), and it pulls the slam_karto.cpp from the slam_gmapping code, which had that license because gmapping WAS CC - but has now been rereleased as BSD.