only add column if it does not exist yet
update changelog, prep for 2.4.2
fix method for generating migration class name
fix lookup of translated columns
remove html postfix...seems obsolete
use end_with, make code more expressive
remove obsolete to_s
fix template name
Merge pull request #245 from screenconcept/features/dont_run_migrations_if_columns_exist

only add column if it does not exist yet