enhanced translate filter

extended translate filter with following features
1) filter_matched is now called on successful translation
2) In case destination field already exists should we skip translation(default) or override it with new translation? Configured with @override
3) treat dictionary keys as regular expressions to match against, used only then @exact enabled. Configured with @regexp
4) Optionally incase no translation was made add default translation. Configured with @fallback
5) dictionary can be also specified inside config as @dictionary hash. If both @dictionary and @dictionary_path are specified , these two dictionaries will be merged.
6) rspec tests