Fix button positioning & Fix image toolbar positioning

@j0k3r fixed the button positioning (i.e. the insert button) when typing text.

Based on @j0k3r 's work, I found that the insert button positioning and the image toolbar positioning still had positioning issue.

For example, as the following images, if there's other html in the front of editor area, the insert button position and image toolbar position have error.
![2014-11-28 9 24 04](https://cloud.githubusercontent.com/assets/4083642/5228439/0b7ae722-7745-11e4-896a-0c82ca83e362.png)
![2014-11-28 9 16 46](https://cloud.githubusercontent.com/assets/4083642/5228441/122c6366-7745-11e4-9e9d-38fd4a36b0ee.png)

The below image is the result after this PR fixes above issues.
![2014-11-28 9 11 59](https://cloud.githubusercontent.com/assets/4083642/5228443/1a572e7c-7745-11e4-8218-33e1447482a5.png)