Adds a safe check, i18n is expecting undefined not null. Fix a method name and translation to be at placeholder.

Removing translateString forces using data-i18n attributes, to make sure we do not forget to set them. Missing data-i18n attributes is a problem with late loading where we can end up without translation, without text. Missing data-i18n attributes is also problem that strings will not be translated when changing language.
Fixes a bug in invite dialog, where remove password button was shown for non moderators.

Converts ConferenceUrl to a class and binds an instance to the global
APP variable, as requested by HTerezov.

We need to make sure that on the page reload all original parameters
used to load the conference are preserved. New modules helps to manage
different types of conference URLs like the one used for invites and
the one for reloading the page.