#1005 Improve restricted user feature (performance, error handling)

- Move check for restricted user into validation service
- Keep restrictions in a map by name for fast lookup, avoid splitting Strings on every call
- Gracefully handle case when entry does not have the expected ';' and log exception

src/test/java/fr/xephi/authme/util/StringUtilsTest.java

@@ -95,4 +95,14 @@ public class StringUtilsTest {
     public void shouldHaveHiddenConstructor() {
         TestHelper.validateHasOnlyPrivateEmptyConstructor(StringUtils.class);
     }
+
+    @Test
+    public void shouldCheckIfHasNeedleInWord() {
+        // given/when/then
+        assertThat(StringUtils.isInsideString('@', "@hello"), equalTo(false));
+        assertThat(StringUtils.isInsideString('?', "absent"), equalTo(false));
+        assertThat(StringUtils.isInsideString('-', "abcd-"), equalTo(false));
+        assertThat(StringUtils.isInsideString('@', "hello@example"), equalTo(true));
+        assertThat(StringUtils.isInsideString('@', "D@Z"), equalTo(true));
+    }
 }