Moterm part 6: Add moterm_example_app.

Moterm part 6: Add moterm_example_app.

This is an example app that is itself embeddable, and in turn embeds a
single moterm. It uses that moterm to prompt the user about what to
connect to (e.g.: mojo:echo_terminal,
mojo:netcat?host=localhost&port=80), and then connects the moterm to
whatever the user enters. After that connection is done (typically
terminated by ^D on a line by itself), it prompts the user again, etc.

R=erg@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/70d849d9e0a9f4fe5ae6dc8751ddd92df0ce66fd

[Elliot Glaysher, 2015-05-11 23:47:45]

lgtm

[viettrungluu, 2015-05-11 23:57:13]

Committed patchset #1 (id:1) manually as
70d849d9e0a9f4fe5ae6dc8751ddd92df0ce66fd (presubmit successful).