Add WDL language support (#3858)

* Add WDL language support

* Add ace mode

samples/wdl/hello.wdl

@@ -0,0 +1,21 @@
+# Sample originally from https://github.com/broadinstitute/centaur
+
+task hello {
+  String addressee
+  command {
+    echo "Hello ${addressee}!"
+  }
+  output {
+    String salutation = read_string(stdout())
+  }
+  runtime {
+    docker: "ubuntu@sha256:71cd81252a3563a03ad8daee81047b62ab5d892ebbfbf71cf53415f29c130950"
+  }
+}
+
+workflow wf_hello {
+  call hello
+  output {
+     hello.salutation
+  }
+}