Fix hyperlink tooltip being covered by nuxeo-html-editor toolbar

When configuring a hyperlink for text at the top of the text area of nuxeo-html-editor, the hyperlink tooltip is covered up by the toolbar and cannot be filled out - the text must be placed lower and then moved up after configuring the hyperlink.

Steps to Reproduce:

1. Create a Note document with HTML format
2. In the nuxeo-html-editor, write text at the top of the text area
3. Highlight the text and click the "Insert Link" button from the toolbar

Expected Behavior: hyperlink tooltip is able to have text configured, is rendered either over the toolbar or below it.

Actual behavior: hyperlink tooltip is covered up by the toolbar and is inaccessible.