tooling: improve dev flag to add pretty-simple conditionnally

gargantext.cabal

@@ -102,7 +102,7 @@ flag no-phylo-debug-logs
   manual: True
 
 
-Flag OnlyWarn
+Flag dev
   Description: More permissive rules during dev
   Default:     False
   Manual:      True
@@ -485,8 +485,10 @@ library
   ghc-options: -Wall -Wincomplete-uni-patterns -Wincomplete-record-updates -Wmissing-signatures -Wunused-binds -Wunused-imports -Wunused-packages -Werror -freduction-depth=300 -fprint-potential-instances
 
   -- But in dev warnings are not errors
-  if flag(OnlyWarn)
+  if flag(dev)
     ghc-options: -Wwarn
+    build-depends: 
+      pretty-simple
 
   hs-source-dirs:
       src
@@ -586,7 +588,6 @@ library
     , patches-map ^>= 0.1.0.1
     , postgresql-simple >= 0.6.4 && <= 0.7.0.0
     , process ^>= 1.6.18.0
-    , pretty-simple
     , product-profunctors ^>= 0.11.0.3
     , protolude ^>= 0.3.3
     , quickcheck-instances ^>= 0.3.25.2