* Add initial support for custom stylesheets
Allow an override file `custom.css` that can partially override the
stylesheet used for the web interface.
# Changes
1. Update default views to use custom stylesheet
2. Update documentation
Related to: https://github.com/Ylianst/MeshCentral/issues/7144
* Add custom style support to more views
Load `custom.css` in the following views:
- agentinvite.handlebars
- invite.handlebars
- login2.handlebars
- message2.handlebars
- messenger.handlebars
- player.handlebars
- sharing.handlebars
