Adding captions to images.

Test Plan:
We tested

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Fixing YouTube plugin to take a YouTube ID and not a full URL.

This fixes a bunch of invalid use cases, like using "/" as the URL
and other inputs that cause unexpected behavior.
Make iframe sizes of Google Spreadsheet & PDF plugins consistent.
Fixing non-inline styling.
Get rid of all non-english language files.

Summary:
This makes ckeditor only usable in English, but removs 680 files from
third_party.zip, which should help webapp startup time.  (The problem
is that any import from third-party has to read third_party.zip, so
the smaller third_party.zip is, the faster that read happens, since
appengine is bobbins for reading files.)

This is pretty much a hack, and I'd like to find a way to get these
files back.  We should feel free to roll back this change if we ever
need these files for anything, and figure out another way to save
start-up time.

Test Plan: Fingers crossed.

Reviewers: tom

Reviewed By: tom

CC: ben

Differential Revision: http://phabricator.khanacademy.org/D4623
Add some newly-enabled plugins to the CKEditor build process.
Replace " with &quot; entity in ckeditors alt text. Also add .arcconfig

Summary:
A few times now translation process has died because of articles
created with this bug in it.  The unescaped quotes before would
end the alt tag and the rest of the alt message would become attributes
on the element. If any of that text was a pure number, then it would
fail to parse as valid html during fake_translation

Test Plan:
./dev/builder/build.sh
From any article, in edit mode add an image that has a quote in the alt text
Check it out in the inspector, to see the alt text showing up correctly.
Publish
Change the src in the inspector, make sure the alt shows correctly

Reviewers: tom

Differential Revision: http://phabricator.khanacademy.org/D5278

Conflicts:
	plugins/image2/plugin.js
Reran ./dev/builder/build.sh

Test Plan:
Loaded an article,
added an image with alt tag with quotes,
checked in inspector that the alt is correct

Auditors: tom
Adding source dialog to the plugin build

I would like HTML edit mode for articles. I'm currently editing by inspecting HTML and changing the content editable element, but that's getting fairly annoying.

Since we use the inline editor mode, the way to do this is actually the "sourcedialog" plugin, not "sourcearea", so I've added that plugin and re-built

Test Plan:
Add 'Sourcedialog' to toolbar and extraPlugins='sourcedialog' to config, see Source show up on toolbar in article editor.
Merge pull request #2 from Khan/pf-add-sourcedialog

Adding source dialog to the plugin build
Add in new CKEDITOR embedded scratchpad plugin.
Add in missing icon file.
Fix custom plugin icons so that they're included in the sprite file. Run a new build.
Bring the scratchpad dialog directly into the plugin to avoid an extra import.
Run a build and bring in the updated scratchpad.js
Adjust the CSS rule to match based on the attribute rather than the class name.
Add in missing placeholder images.
Adding sourcedialog.js
Merge pull request #3 from Khan/pf-add-folder

Adding sourcedialog.js
Make the default width equal to 100%. Fixes T2074.