Do not raise ArgumentError if translation key is nil.
Converts all dasherized translation keys into symbols.

We changed the behavior of the automatic default value for missing translation keys. Only if the key is a symbol it gets humanized. So, now one can pass a string that will be used as default, if no translation is found.
Setting manual defaults for translations having string as key.
Fix z-index of pagination.
Display warning icon, if image could not be loaded.
Bump version to 2.6.0.rc3