AdminForm: Error message when addin is not valid
AssemblyManager: Release AppDomain and unzip package with .exe inside.
ShutdownEvent: proper event unbinding.

Before destroying addin AppDomain, all events should be unbound. To do so we
first need to unbind it and then call shutdownEvent.Set().

It`s also necessary to unbind FormEvents, that wasn`t done before.

To prevent thread syncronization issues, Framework forms are not registered,
even if they`re UserForm.
AssemblyManager: MD5SUM not consider i18n resources as part of it.
AssemblyManager: Moved Assembly specific loading to separate AppDomain.

This way we guarantee that after we use this Assembly, we can unload it.