loxi_frontend: move classes only used by c to c_gen

 - flags
 - identifiers
 - match
 - translation
 - type_maps

were only used by the c backend. I'm moving them to c_gen to
unclutter the loxi_front_end space (and updating references
in the c backend)
diff --git a/c_gen/c_show_gen.py b/c_gen/c_show_gen.py
index 0ec81b4..fe3e3dc 100644
--- a/c_gen/c_show_gen.py
+++ b/c_gen/c_show_gen.py
@@ -34,12 +34,13 @@
 
 import sys
 import of_g
-import loxi_front_end.match as match
-import loxi_front_end.flags as flags
+import c_gen.match as match
+import c_gen.flags as flags
 from generic_utils import *
-import loxi_front_end.type_maps as type_maps
+import c_gen.type_maps as type_maps
 import loxi_utils.loxi_utils as loxi_utils
-import loxi_front_end.identifiers as identifiers
+import c_gen.loxi_utils_legacy as loxi_utils
+import c_gen.identifiers as identifiers
 from c_test_gen import var_name_map
 
 def gen_obj_show_h(out, name):