Make filter object of any type, not only String

[davideas]

Reason of the improvement

Give the possibility to apply a multi filter simultaneously on more fields.

Impact

It will have an impact on IFilterable signature, so the filter() method can accept a custom type.
New methods will substitute the current when managing the filter:

Old methods		New methods
setSearchText(String)	=>	setFilter(Serializable)
String getSearchText()	=>	Serializable getFilter()
boolean hasSearchText()	=>	boolean hasFilter()
`boolean hasNewSearchText(String)	=>	boolean hasNewFilter(Serializable)

If filter object is of type String, automatic trim and lowercase is maintained when setting it.
Must be of type Serializable in order to maintain save/restore instance state on configuration changes. String it is.

⚠️ Note: Old methods will be removed from next release.

[davideas]

Example with simple text:

public class ... extends ... implements IFilterable<String> {
    @Override
    public boolean filter(String constraint) {
        return getTitle() != null && getTitle().toLowerCase().trim().contains(constraint);
    }
}

Example with custom type (multi filter)

It's your choice to implement an inclusive (any match) or exclusive (all match) filter, here an exclusive example is shown:

public class ... extends ... implements IFilterable<MyFilter> {
    @Override
    public boolean filter(MyFilter constraint) {
        boolean result = true;
        if (constraint.isElectricCarSet()) {
            result = this.electric == constraint.isElectric());
        }
        if (result && constraint.isPriceSet()) {
            result = this.price <= constraint.getPrice());
        }
        return result;
    }
}