fix(fineuploader.css): set z-index of qq-edit-filename input element

It appears that the <input> element with class qq-edit-filename is being placed
above (in terms of z-index) the 'Cancel' or 'Delete' buttons on the DOM.

fixes #925
fixes #926
chore(*): Version bump

3.7.0 -> 3.7.1
chore(README.md): Increment date

Corresponds to recent hotfix release 3.7.1