fix: change all theme references to use --oscd-theme-*

[stee-re]

Shell was making a lot of references to --oscd-base* etc instead of referencing --oscd-theme-* making it impossible to override the theming. Furthermore the colours were hardcoded into the shell itself - which was completely wrong.
The colours and "theming" have been moved to the demo and the shell now only refers to --oscd-theme-* variables

Whats changed:

• Shell (and relatives) reference only oscd-theme-* variables
• Setting of theme variables is done within the scope of the demo
• The only -md-* veriables set within the shell, are variables the shell requires - others have been moved to the /demo for reference.