Added new criteria 'tiling' / 'floating'. (#2481)

These criteria allow selecting only windows in a specific mode, i.e.,
tiling and floating, respectively.

fixes #2406

parser-specs/commands.spec

@@ -53,6 +53,8 @@ state CRITERIA:
   ctype = 'title'       -> CRITERION
   ctype = 'urgent'      -> CRITERION
   ctype = 'workspace'   -> CRITERION
+  ctype = 'tiling', 'floating'
+      -> call cmd_criteria_add($ctype, NULL); CRITERIA
   ']' -> call cmd_criteria_match_windows(); INITIAL
 
 state CRITERION:

parser-specs/config.spec

@@ -173,6 +173,8 @@ state CRITERIA:
   ctype = 'title'       -> CRITERION
   ctype = 'urgent'      -> CRITERION
   ctype = 'workspace'   -> CRITERION
+  ctype = 'tiling', 'floating'
+      -> call cfg_criteria_add($ctype, NULL); CRITERIA
   ']'
       -> call cfg_criteria_pop_state()