Allow having <img attributes> in text formats

Problem/Motivation

If a text format allows having <img> tags but only with specific attributes (like <img src width height alt>), Insert module throws a dialog saying The selected text format will not allow it to display images. The text format will need to be changed for this image to display properly when saved.

Proposed resolution

Remove the closing angle bracket in ImageInserter.js (ie. don't look for <img> but only <img).

Remaining tasks

Implement, patch, test, commit.

User interface changes

None.

API changes

None.

Data model changes

None.