Added ignores

Ignoring an OS-X file (._.DS_Store) and the thrash folder generated in
inc/template
Rewritten document.hidden to document.hiddenElement

As of FireFox 18 'document.hidden' is used to show if a tab is visible
or not.

"Returns true if the page is in a state considered to be hidden to the
user, and false otherwise."
Source:
https://developer.mozilla.org/en-US/docs/DOM/Using_the_Page_Visibility_API