Incorrect comparision in BankCodeStructure#isCharacterType()

Method `BankCodeStructure#isCharacterType()` checks whether `IbanCharType` is numeric, while the method's name suggests it should be comparing against `a` or `c`.

```java
@JsonIgnore
public boolean isCharacterType() {
return BbanStructureEntry.EntryCharacterType.n == getType();
}
```

```java
public enum EntryCharacterType {
/** Numerical digits (0-9 only) */
n,
/** Alphabetical characters (A-Z only) */
a,
/** Combined alphabetical (uppercase) and numeric characters (A-Z and 0-9) */
c
}
```