Fix: Unicode errors in objectbrowser forms

Several places in objectbrowser forms have string formatting
in the form of "%s" % variable which is subject to UnicodeDecodeError
when variables contain non ascii character.

We workaround that by calling smart_str() around dangerous variable names.

Fixes #404
objectbrowser/forms.py: Minor cleanup

Ran code inspection on file and did minor cleanup.
Merge pull request #468 from opinkerfi/fix-unicode-errors-in-objectbrowser-form

Fix unicode errors in objectbrowser form