localization demo + bug fix

- had missed 3 hardcoded strings, moved them to res/values/strings.xml
- created values-es-rUS folder for American Spanish with strings.xml of
translated words
- also contains notes and tips for lecture/demo
- fixed bug in WorkoutsAdapter line 43 that caused crash, switched from
parent to null (warning persists but doesn't crash now)
Merge pull request #4 from nerychapeton/localization-demo

localization demo + bug fix