Add option to disable Google Fonts and load fonts locally

[LukasJoswiak]

There is an existing flag disablefancyfonts that turns off loading fonts via Google Fonts. I wanted to keep using these fonts, but didn't want to make a request to Google to load them.

This PR adds an additional flag, disablegooglefonts which can be set to true to load fonts from the server instead of making a request to Google Fonts.

Example (config.toml):

[params]
disablefancyfonts = false
disablegooglefonts = true

The disablegooglefonts flag only has an effect when disablefancyfonts is set to false. disablegooglefonts defaults to false.