Use RandomString for IPB4 implementation; minor documentation

- Improve RandomString and create new generateLowerUpper method
- Add documentation to the IPB4 class to explain why the salt is stored twice

src/test/java/fr/xephi/authme/security/RandomStringTest.java

@@ -44,6 +44,22 @@ public class RandomStringTest {
         }
     }
 
+    @Test
+    public void shouldGenerateRandomLowerUpperString() {
+        // given
+        int[] lengths = {0, 1, 17, 143, 1808};
+        Pattern badChars = Pattern.compile(".*[^0-9a-zA-Z].*");
+
+        // when / then
+        for (int length : lengths) {
+            String result = RandomString.generateHex(length);
+            assertThat("Result '" + result + "' should have length " + length,
+                result.length(), equalTo(length));
+            assertThat("Result '" + result + "' should only have characters a-z, A-Z, 0-9",
+                badChars.matcher(result).matches(), equalTo(false));
+        }
+    }
+
     @Test(expected = IllegalArgumentException.class)
     public void shouldThrowForInvalidLength() {
         // given/when

src/test/java/fr/xephi/authme/security/crypts/IPB4Test.java

@@ -1,13 +1,18 @@
 package fr.xephi.authme.security.crypts;
 
+import fr.xephi.authme.ConsoleLoggerTestInitializer;
 import fr.xephi.authme.util.WrapperMock;
 import org.junit.BeforeClass;
 
+/**
+ * Test for {@link IPB4}.
+ */
 public class IPB4Test extends AbstractEncryptionMethodTest {
 
     @BeforeClass
     public static void setUpSettings() {
         WrapperMock.createInstance();
+        ConsoleLoggerTestInitializer.setupLogger();
     }
 
     public IPB4Test() {