Bael 1404 kotlin (#4033)

* add article files

* update kotlin version in pom

* IntelliJ added binary folder to all the .gitignores

* IntelliJ added binary folder to all the .gitignores

* update test function names

* Expand tests and add more code for more meaningful content within the article.
Remove core-kotlin from parent pom again for eclipse to work.

* adjust for issues with custom-pmd

* rename test

* Revert "IntelliJ added binary folder to all the .gitignores"

This reverts commit 0850a2a.

* Revert "IntelliJ added binary folder to all the .gitignores"

This reverts commit 2b17cf2.

* renamed test to match article

core-kotlin/src/test/kotlin/com/baeldung/filter/DistinctTest.kt

@@ -7,7 +7,7 @@ internal class DistinctTest {
     data class SmallClass(val key: String, val num: Int)
 
     @Test
-    fun givenArrayOfSomeDuplicateValues_whenApplyingDistinct_thenReturnListOfNoDuplicateValues() {
+    fun whenApplyingDistinct_thenReturnListOfNoDuplicateValues() {
         val array = arrayOf(1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 5, 6, 7, 8, 9)
         val result = array.distinct()
         val expected = listOf(1, 2, 3, 4, 5, 6, 7, 8, 9)