New data for Lassa - Githubissues

This PR includes updated Lassa data folling an updated literature search. The articles, outbreaks, models and parameter csv files have been updated.

Checklist:

[ X] I have added new dependencies in DESCRIPTION
[ X] I have bumped the version number in DESCRIPTION
[X ] I have updated the NEWS.md
[X ] I have added unit tests using testthat
[X ] I have checked that the package can install locally using devtools::install_local("<path-to-epireview>")
[X ] I have added documentation where required
[ X] My documentation includes examples of how to use the function
[X ] If necessary, I have updated priority-pathogens

mrc-ide / epireview