Improve tex-naming

[Aypac]

Each cells name is converted to be Tex-compatible. Right now, all non '\w' characters are removed and all spaced replaced by and underscore. To prevent duplicate names, we include a hash of the original name at the end of each name.

• This hash is a quick hack and can be improved
• The replacing rules could be a bit more clever
• This does not entirely prevent possible duplicate names