Update antlr dependency from 4.5.3 to 4.7.1 switch to gradle in idl2k

This is a squashed and rebased commit of https://github.com/JetBrains/kotlin/pull/1945

- add idl2k to default gradle build lifecycle
- removemaven build completely
- invert maven's `idl2k.deploy.skip` to `idl2k.deply` in gradle
(false by default)
- antlr upgrade from 4.5.3 to 4.7.1 - I'd have to slightly modify WebIDL.g4 definition though -
and updated copyright accordingly - my updates were based on
https://raw.githubusercontent.com/antlr/grammars-v4/master/webidl/WebIDL.g4
- I've checked all generated output to make sure it is identical to
what we hade before dependency update.
- Package idl2k according to our souce code guidelines

libraries/pom.xml

@@ -79,8 +79,6 @@
 
         <module>tools/maven-archetypes</module>
 
-
-        <module>tools/idl2k</module>
         <module>tools/kotlin-annotation-processing-maven</module>
         <module>tools/kotlin-maven-allopen</module>
         <module>tools/kotlin-maven-noarg</module>