Remove obsolete HTML tags

[ghamerly]

Right now problemtools generates the following HTML tags which are considered obsolete, and should be handled by CSS:

• <tt>
• <big>
• <u>
• <center>

Reference: https://dev.w3.org/html5/pf-summary/obsolete.html

These are defined in the zpts files of https://github.com/Kattis/problemtools/tree/develop/problemtools/templates/html, specifically:

• https://github.com/Kattis/problemtools/tree/develop/problemtools/templates/html/Alignment.zpts
• https://github.com/Kattis/problemtools/tree/develop/problemtools/templates/html/FontSelection.zpts
• https://github.com/Kattis/problemtools/tree/develop/problemtools/templates/html/ulem.zpts
• https://github.com/Kattis/problemtools/tree/develop/problemtools/templates/html/Verbatim.zpts