6224 bug keep greek letters in extracted model somehow

[YohannParis]

Description

• Added extra var[...] names of greek letters.
• Add a method to ModelService to clean up greek letters.

Resolves #6224

Testing

In a new create model from equations used the following LaTeX equations, and verify that the names of variables with a greek id have their name updated with a greek unicide character.

 \frac{d S(t)}{d t} = - \beta * S(t) * I(t) - \mu
 \frac{d I(t)}{d t} = \beta * S(t) * I(t) - \gamma * I(t) - \mu
 \frac{d R(t)}{d t} = \gamma * I(t) - \mu

[liunelson]

Thanks for adding the var* edge cases!