feat(jedi.lua): enable call signatures in Jedi completion popup and configure Jedi to use spaces instead of tabs for indentation

feat(supertab.lua): add Supertab plugin and configure it to be loaded after Absolute configuration

lua/absolute/plugins/supertab.lua

@@ -0,0 +1,6 @@
+return {
+    "ervandew/supertab",
+    config = function()
+        require("absolute.after.supertab")
+    end
+}