Add utility class to interact with page sources

[voievodin]

What does this PR do?

Adds utility methods to interact with pages of elements.

Example:
For the class:

class MyDao {
    Page<MyObject> getObjects(int items, long skip) { 
    // ... 
    }
}

Pages utilities allow to simply iterate through the elements as if there are no pages at all.

MyDao instance = ...

// iterating through pages
for (MyObject obj : Pages.iterate(instance::getObjects)) {
    // ...
}

// iterating through pages with items per page configuration
for (MyObject obj : Pages.iterate(instance::getObjects, 20)) {
    // ...
}

// lazily iterating through pages
for (MyObject obj : Pages.iterateLazily(instance::getObjects)) {
    // ...
}

// lazily iterating through pages with items per page configuration
for (MyObject obj : Pages.iterateLazily(instance::getObjects, 20)) {
    // ...
}

// getting stream of objects
Pages.stream(instance::getObjects)

// getting stream of objects  with items per page configuration
Pages.stream(instance::getObjects, 20)

// getting stream based on lazy iterator
Pages.streamLazily(instance::getObjects)

// getting stream based on lazy iterator with items per page configuration
Pages.streamLazily(instance::getObjects, 20)

Changelog

Added new utility methods for handling pagination of objects.

Release Notes

N/A

Docs PR

N/A

[codenvy-ci]

Build success. https://ci.codenvycorp.com/job/che-pullrequests-build/2047/

[codenvy-ci]

Build success. https://ci.codenvycorp.com/job/che-pullrequests-build/2048/

[JamesDrummond]

What are "pages" in regards to this utility? Can you provide a use case example?

[voievodin]

Page doc.

e.g. code can be changed to

for (Member member : Pages.iterate((max, skip) -> dao.getMembers(orgId, max, skip)) {
    dao.remove(member.getUserId(), member.getOrganizationId());
}