add convenience function to extract translations

Adds phase awareness in this function. Closes #349.
gtlua: add feature_node:extract_and_translate_sequence()
reintroduce non-mandatory joining
gtlua: make join a parameter again
gtlua: extend documentation of FeatureNode bindings
move around Lua method implementations, add __eq and __tostring

Closes #352.
add simple testcase for phase aware translation