[repo/push] --use-json to convert podspecs to JSON format when pushing

Fix linting with Xcode 8

That version offers the ability to look for the oldest simulator
available for a particular OS, so that we do not have to hardcode device
names anymore.

- Uses 'iPhone 5' for linting iOS projects, because there is no 4s
  anymore
- Uses an updated version of `fourflusher` which can parse two-digit OS
  versions (hello iOS 10.0)

[UI] Ensure printing a path does not raise

[Installer] Embed Pods Frameworks in UI Tests

fixes https://github.com/CocoaPods/CocoaPods/issues/5250

Move Pods Project Generation into an Xcode namespace

[PodTarget] Make #recursive_dependent_targets handle cyclic dependencies

[Cache] Use `git ls-remote` to skip full clones for branch dependencies

[Travis] Add Ruby 2.3 to matrix

Fixes #5362

Fix minimum deployment target error for local pods.

When resolver fails because of platform deployment target for a local pod,
`possibility` value is non-nil. We use this to discriminate this error type with
conflict caused by a change in dependencies of the local pod.

Use `require` instead of `autoload` for fourflusher

Fixes #5445

This adds the posibility of caches hits for git branch depedencies.
Previously, since pods didn't know the commit the branch points it
always did a full clone of the repo. Using `ls-remote` we can check the
commit the branch points to and reuse cached version of the pods if
available.

[Validator] Support linting pods that link against XCTest

* Fix Dangerfile Rubocop violations

* Update CHANGELOG.md

* Update docs

* Don't use Type = Type::Type in tests

use `pr_title` instead of `pr.title` in Dangerfile

[Setup] Allow running with --silent

Added rake task to check submodules

[PodTarget] Allow non-deduped targets to be frameworks