Add theme: floating side bar

[mauro-balades]

Add theme: floating side bar

This PR adds a new theme to the theme library.

Theme Details

• Name: floating side bar
• Description: A Zen browser mod for a detached and redesigned the sidebar, so that it appears to float and match the zen aesthetic.
• Homepage: https://github.com/princess-wawa/zen-floating-side-bar
• Author: @princess-wawa

[princess-wawa]

For it to currently work on twilight, the lines 37-44 have to be changed from

#sidebar-box[positionend="true"]{
 right: 0.6vw !important;
 left: unset !important;
}
#sidebar-box:not([positionend="true"]){
  right: unset !important;
  left: 0.6vw !important;
}

to

#sidebar-box[positionend=""]{
 right: 0.6vw !important;
 left: unset !important;
}
#sidebar-box:not([positionend=""]){
  right: unset !important;
  left: 0.6vw !important;
}