add default value to summary

[otaviojava]

The proposal are reduce the number of methods to get a summary, considering that not make sense have two filters when it was already defined in summarizing Monetary method, so:
from:

  MonetarySummaryStatistics summary = getCurrencies().stream()
            .filter(MonetaryFunctions.isCurrency(DOLLAR))
            .collect(MonetaryFunctions.summarizingMonetary(DOLLAR));

to:

 MonetarySummaryStatistics summary = getCurrencies().stream()
            .collect(MonetaryFunctions.summarizingMonetary(DOLLAR));

Another changes was the creation of a decoration to group summary, this way when a currency that was not summarizing, now will return an empty summary instead of a null.

👼 Test passed