Fix two problems in runtime error dialog within Blocks Editor

Problem 1: As illustrated in Ghica's "Blocks disappearing" email, HTML from an
error message could end up being rendered in a runtime error dialog. This
commit property escapes the HTML so that it is not rendered.

Problem 2: As illustrated in Ghica's "Blocks disappearing" email, an error
message could be so large that the runtime error dialog could fill the
entire blocks workspace. This commit adds a "blocklyRuntimeErrorDialog"
CSS class to the runtime error dialog that limits the window to no more
than 75% of the width and height of the blocks workspace, and makes the
contents scrollable if it's too big.

Change-Id: I4150c11aa93f6b10d8cee657b30141671d2f9050
Add a “Companion Information” Item to the Help Menu.

Provides a Download URL for the Companion that matches this version as
well as a QR Code that can be scanned by a browser (or the current
Companion) to install the Companion directly on a device.

Change-Id: Ie10c841aa8ef6845fb586cd49024df199f0cd09d
Change Twitter component to send pictures to Twitter.

Change Twitter component to send pictures to Twitter instead of
TwitPic.  Adds Toast with feedback if Image is not valid and the
update is not sent.

Change-Id: I8ef22d1307ed5bcd8008d44951ec6f1815eac045