[core] Rework core implementation

Experimental re-implementation of core functionality with the aim:
- Depend only on the Python Standard Library for core
- If modules are missing elsewhere, *never* throw
- Unit test *everything*
- Cleaner and more minimal implementation
- Better integration points for existing implementations (charts,
  braille, etc.)
- Full backwards-compatibility with existing module system (except where
  modules can be vastly simplified)

themes/sac_red.json

@@ -1,59 +0,0 @@
-{
-	"icons": [ "paxy97", "awesome-fonts" ],
-	"defaults": {
-		"warning": {
-			"fg": "#FDFFFC",
-			"bg": "#B91372"
-		},
-		"critical": {
-			"fg": "#FDFFFC",
-			"bg": "#FF0022"
-		},
-		"default-separators": false,
-		"separator-block-width": 0
-	},
-	"cycle": [
-		{
-			"fg": "#FDFFFC",
-			"bg": "#990014"
-		},
-		{
-			"fg": "#FDFFFC",
-			"bg": "#011627"
-		}
-	],
-	"battery": {
-		"charged": {
-			"fg": "#FDFFFC",
-			"bg": "#41EAD4"
-		},
-		"AC": {
-			"fg": "#FDFFFC",
-			"bg": "#41EAD4"
-		}
-	},
-  "bluetooth": {
-      "ON": {
-			    "fg": "#FDFFFC",
-			    "bg": "#41EAD4"
-      }
-  },
-  "cmus": {
-  	"bg": "#C42021"
-  },
-    "pomodoro": {
-        "paused": {
-            "fg": "#FDFFFC",
-            "bg": "#B91372"
-        },
-        "work": {
-            "fg": "#FDFFFC",
-            "bg": "#41EAD4"
-        },
-        "break": {
-            "fg": "#FDFFFC",
-            "bg": "#011627"
-        }
-    }
-
-}