Clean more tex strings in project report generation

[pritpaul]

https://github.com/tbpmig/mig-website/blob/663525f0ea241cd150d7aaeba7eee90a543970d4/history/models.py#L1071

We just ran into an issue with a "#" in the problems encountered field. Probably all user-input strings should be cleaned.

Also, not sure if useful but I found a more complete list of replacements: https://stackoverflow.com/questions/16259923/how-can-i-escape-latex-special-characters-inside-django-templates

[mikehand]

Won't be fixed in time. Please work around

[pritpaul]

already did :) just wanted to report it for future consideration