JavaScript syntax highlighting support for product versions 2019.2 (#78)

JetBrains product versions  2019.2 introduced support for 20+ languages
(1) out-of-the-box by integrating TextMate (2) schemes.
Unfortunately this resulted in a change for existing theme definition
where some editor color scheme keys that previously inherited the best
matching global key now used the attributes defined by the parent theme
"Darcula". Therefore Nord's highlighting for JavaScript broke and
required to explicitly define the values for some attributes in order to
achieve the same highlight like in previous versions that are matching
Nord's style guidelines:

- `JS.GLOBAL_FUNCTION` — Map to `DEFAULT_FUNCTION_DECLARATION`
- `JS.GLOBAL_VARIABLE` — Map to `DEFAULT_GLOBAL_VARIABLE`
- `JS.INSTANCE_MEMBER_FUNCTION` — Map to `DEFAULT_INSTANCE_METHOD`

References:
  (1) https://www.jetbrains.com/idea/whatsnew/#v2019-2-editor
  (2) https://macromates.com

Resolves GH-77

resources/themes/nord.xml

@@ -1055,6 +1055,9 @@
     </option>
     <option name="JAVA_KEYWORD" baseAttributes="DEFAULT_KEYWORD" />
     <option name="JAVA_VALID_STRING_ESCAPE" baseAttributes="DEFAULT_VALID_STRING_ESCAPE" />
+    <option name="JS.GLOBAL_FUNCTION" baseAttributes="DEFAULT_FUNCTION_DECLARATION" />
+    <option name="JS.GLOBAL_VARIABLE" baseAttributes="DEFAULT_GLOBAL_VARIABLE" />
+    <option name="JS.INSTANCE_MEMBER_FUNCTION" baseAttributes="DEFAULT_INSTANCE_METHOD" />
     <option name="JS.REGEXP">
       <value>
         <option name="FOREGROUND" value="ebcb8b" />