math: adhere to Hugo's default config params

[McShelby]

With the passthrough configuration it is necessary to force load the MahtJax library on the client side.

Hugo's documentation gives a math=true param in its examples while the theme wants to have disableMathJax=false.

Besides the double negation it is also desirable to have the theme parameter named the same way as in Hugo's docs.

And while changing it for the math shortcode, the same parameter for the openapi and mermaid shortcode should be changed aswell.