Minor update to the message logged when multiple devices are connected with no device ID specified

Example of setting the content type of a POST request

Input asserts while keyboard is dismissed

Now we recreate the stub every time we try to connect to the keyboard. The
underlying message pipe in the stub cannot be re-used, which is why we
previously asserted.

Fixes #776

Avoid launching Xcode after "flutter ios --init"

Add RawKeyboardListener

RawKeyboardListener makes it easier to listen for raw keyboard events.

Fixes #787

flutter start shouldn't log xcodebuild output

Hide EditableString implementation details

Previously, EditableString had many public members because it needed to
implement the KeyboardClient interface. However, that's confusing
because these methods cannot be called directly.

Now EditableString holds a private implementation of the KeyboardClient,
which hides the implementation details.

Fixes #208
Fixes #209

Xcodebuild produces a lot of output that isn't relevant to developers. We
should hide it by default.

improve device notification support

Keyboard service doesn't commit the last edit when it's dismissed

We were getting the proper values, but we thought we were still composing, so
the text was still underlined.

Fixes #115

Support local paths to third-party jars in flutter apk.

Improve error messages for iOS workflow

This reverts commit b240cda8.

We now check that you've got an "ios" directory and that you have the proper
version of Xcode.

Also improve the error message a bit if a download fails.

get a bug fix for multi-line command descriptions

_getPadding was ignoring its argument

Reimplement Inherited.notifyDescendants to use a registration list

...instead of a deep walk.

Add material design features to Input

That way folks can customize it if they want (and it makes the code a
bit more self-documenting).

Now the label animates from its inline position to above the text and
the focus highlight grows into place.

RawEditableLine is now responsible for the scrolling behavior, which
removes the need for callbacks between RawEditableLine and Input. It
also fixes a bug whereby the whole Input widget (including its icon)
would scroll when the text got long.

Properly support labels, hints, icons, and custom typography.

This reverts commit ab300634.

Make `flutter list` not crash on linux.

Turns out linux does have an ideviceinstaller package
however it doesn't contain idevice_id or any of the
other tools we use.  Furthermore we don't have
xcrun or the rest of xcode on linux so we can't
manipulate simulators either.

No sense in printing out a warning that ios isn't supported
every time on linux, so I wrapped that block in osx only.

@chinmaygarde @devoncarew