js: implement import/delete Key, some fixes

--

* Keyring.js
   - implemented importKey: importing one or more armored public key
     blocks.
   - implemented deleteKey: deleting a public Key from gpg.

* Key.js renamed property Key.armor to Key.armored

* Helpers.js: toKeyIDArray does not complain anymore if there are no
  keys. Not having Keys in e.g. signing keys in encrypt is legitimate
  and common, the complaints were getting spammy

* Errors.js: gpgme_errors now always pass an optional additional
  message, for easier debugging in minified code

* Connection.js: Fix in gpgme-json responses containing objects

* eslintrc.json: Start using eslint. A cleanup to conform to it is not
  done yet

* Added further tests for the new functionality

1 files changed, 6 insertions, 2 deletions

diff --git a/lang/js/src/Errors.js b/lang/js/src/Errors.js
index 3b53eeb4..2f2bfd5c 100644
--- a/lang/js/src/Errors.js
+++ b/lang/js/src/Errors.js
@@ -74,7 +74,7 @@ const err_list = {
     'KEY_NO_INIT': {
         msg:'This property has not been retrieved yet from GPG',
         type: 'error'
-    }
+    },
     // generic
     'PARAM_WRONG':{
         msg: 'Invalid parameter was found',
@@ -118,7 +118,11 @@ class GPGME_Error extends Error{
         if (code === 'GNUPG_ERROR' && typeof(msg) === 'string'){
             super(msg);
         } else if (err_list.hasOwnProperty(code)){
-            super(err_list[code].msg);
+            if (msg){
+                super(err_list[code].msg + "--" + msg);
+            } else {
+                super(err_list[code].msg);
+            }
         } else {
             super(err_list['GENERIC_ERROR'].msg);
         }