Option to disable writing settings block

[lajoiemedia]

Added boolean config setting write_settings_block to allow the skipping of adding a settings block to the illustrator document. This is a useful feature when automating ai2html, since ai2html-config.json becomes the single source of truth for settings.

This was the problem I was encountering:

I run ai2html with an automation script. When I ran my script with a fresh new AI file, my automation script would use settings from ai2html-config.json. But subsequent runs would ignore changes to that file in favor of the settings blocks now located in the AI file.

With this change, settings are always sourced from ai2html-config.json, no matter the number of times I run my automation script.