getStreamImg: bugfix 'variable referenced before assignment'

bug was introduced sometime during or before 79fd704f59d2befc85303190c2a21a3ce85fb128

Error:
  File "C:\workspace_physical\appengine\bilderapp\bilder.py", line 281, in getStreamImg
    range = len(imgList)
UnboundLocalError: local variable 'imgList' referenced before assignment
class Stream: adding counters for images and views
create stream form: adding more defaults
refactor: renamed Guestbook to CreateStreamService
refactor: CreateStreamService - changed indentation
refactor: CreateStreamService - merging in form generation

Not switching over yet; still serving the form from 'main'
refactor: finalised refactoring of CreateStreamService

* converted 'MainPage' to simple landing page by removing all form generation
* added 'Home'->'/' href to navigation
CreateStreamService: adding description
ViewAllStreamsService initial json implementation