-Subscript and superscript removed
-Creating a new article functional

Test Plan:
Open article
Test that buttons work as expected
Make new article, edit it and save.

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Removed unnecessary plugin buttons and fixed article creation

Summary:
Removed plugins list, superscript, and subscript
Creating a new article now functional

Test Plan:
Open article
play with buttons
create a new article, edit and save

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same as before

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<see below>

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Reviewers: tom

Reviewed By: tom

Differential Revision: http://phabricator.khanacademy.org/D2683