Focus input fields when creating new elements in the configuration UI

[mariusoe]

When a user adds a new file or directory using the configuration UI, it can be done using the buttons located above file tree. Pressing them will open a new dialog containing an input element for entering the name of the file or directory.

It will make the creation of such element easier when the input field gets the brower's focus, thus, the user can immediately start typing without having to select the input field first.