Language simplification for context menu items

Partly Resolves #11714

The extra's authors will need to adjust their lexicons accordingly, as this PR only cover MODX's core lexicon for resources.

![11714-modx-bug](https://cloud.githubusercontent.com/assets/114390/4612589/8617ab5e-52ca-11e4-88e6-1510b832d3fd.png)