feat(workspaces): switch from persp-mode to tar-bar-mode and desktop

Replace persp-mode with:

- tab-bar-mode for perspective/screen management
- desktop-save-mode for session management

Both tab-bar-mode and desktop are enhanced and customized a decent bit
via the siren-tab-bar and siren-desktop modules.

core/siren-core-modules.el

@@ -113,7 +113,8 @@
 (require 'siren-zoom-window)
 
 ;; Workspace management
-(require 'siren-persp-mode)
+(require 'siren-tab-bar)
+(require 'siren-desktop)
 
 ;; Org-mode
 (require 'siren-htmlize)