Change 'Run Application' -> 'Run' and 'Open Folder' -> 'Import Folder'

Re 'Run Application': given Spark's current capabilities, it's a misnomer in many situations, e.g. when the item being "run" is a Polymer element's demo, or just a single HTML file in the hierarchy of an app, etc.
Changed "Import Folder" -> "Add Folder to Workspace" per review discussion
Merge pull request #2276 from ussuri/fix-menu-item-titles

Change 'Run Application' -> 'Run' and 'Open Folder' -> 'Import Folder'