Move inline styling in page files to dedicated css files

Instead of styling defined inside a page file, these settings are now kept in a dedicated css file. This has several advantages:

- It comes much easier to maintain styling, all css files are easy to find and update
- Browser can cache css files, which may improve page loading time
- Separate theme css files exist, no more need to make selection by coding

- This PR is a 1-to-1 move of existing inline styling to css files
- In future more optimization can be made by consolidating css files

emhttp/plugins/dynamix/sheets/Syslinux.css

@@ -0,0 +1,3 @@
+div.basic{display:block}
+div.advanced{display:none}
+textarea.raw{resize:none;font-family:bitstream;width:65.5%}