Make code compatible with java8 date api

[msangel]

Currently the java.time.Instant class is not recognized as date type. Also it would be nice to have compatible api. The library have java7 compatibility so we cannot use Instant in it, but we should provide east way to plug it in.

[msangel]

Sample usage after applying fix:

Filter.registerFilter(Date.withCustomDateType(new Date.CustomDateFormatSupport<Instant>() {
            @Override
            public Long getAsSeconds(Instant value) {
                return value.getEpochSecond();
            }

            @Override
            public boolean support(Object in) {
                return Instant.class.isInstance(in);
            }
}));

Note: this will override old date type, so if you want to have multiple new supported types, this support should be made in scope of one overridden instance.