fix for "undefined" showing up in the dashboard on the TIME SPENT widget...

....  This commit only fixes it for the US English translation, though.  To fix it for the other translations, a string named "common.year.abrv" needs to be added to the other language dashboard_*.properties files.

Bug references:
https://github.com/Countly/countly-server/issues/88
http://support.count.ly/discussions/problems/282-some-of-ui-elements-are-undefined

This commit also contains a fix for a separate minor misspelling error in the US English translation.