Replace raw HTTP dispatch with typed Servant API

nuthatch.cabal

@@ -23,6 +23,12 @@ common shared
     TupleSections
     NamedFieldPuns
     FlexibleContexts
+    FlexibleInstances
+    DataKinds
+    TypeOperators
+    TypeFamilies
+    MultiParamTypeClasses
+    UndecidableInstances
 
   ghc-options:
     -Wall
@@ -51,6 +57,8 @@ common shared
     , http-client           >= 0.7 && < 0.8
     , http-client-tls       >= 0.3 && < 0.4
     , http-conduit          >= 2.3 && < 2.4
+    , http-api-data         >= 0.7 && < 0.8
+    , http-media            >= 0.8 && < 0.9
     , http-types            >= 0.12 && < 0.13
     , memory                >= 0.18 && < 0.19
     , mime-types            >= 0.1 && < 0.2
@@ -59,6 +67,8 @@ common shared
     , postgresql-simple     >= 0.7 && < 0.8
     , resource-pool         >= 0.4 && < 0.5
     , scientific            >= 0.3 && < 0.4
+    , servant               >= 0.20 && < 0.21
+    , servant-server        >= 0.20 && < 0.21
     , stm                   >= 2.5 && < 2.6
     , temporary             >= 1.3 && < 1.4
     , text                  >= 2.0 && < 2.2
@@ -77,6 +87,7 @@ library
   hs-source-dirs:  src
   exposed-modules:
     Nuthatch
+    Nuthatch.Api
     Nuthatch.App
     Nuthatch.Audit
     Nuthatch.Config