Moved Iterators and Iterables from package 'util' to package 'collection'

--HG--
rename : src/org/pitaya/util/Iterables.java => src/org/pitaya/collection/Iterables.java
rename : src/org/pitaya/util/Iterators.java => src/org/pitaya/collection/Iterators.java
rename : test/org/pitaya/util/IterablesTest.java => test/org/pitaya/collection/IterablesTest.java
rename : test/org/pitaya/util/IteratorsTest.java => test/org/pitaya/collection/IteratorsTest.java