Fixed buttons position

[nepsilon]

When composing a long document, we need to scroll all the way to the top to be able to click the read or write buttons.
User experience could be improved by having them fixed at the top.

<button class="write-only-button ss-write"></button> and <button class="read-only-button ss-view"></button> buttons should be set position: fixed.

This is not need for the add and menu buttons, as the user would seldom use them.