Assembly holder no longer needs to be secured.

Assembly holder is no longer secured/unsecured to simplify stuff and to avoid confusion about not being able to use the holder in some cases b/c it's unsecured. Screwdrive now disassemble it and attack_self to interact with its parts.
Also, adding feedback message when trying to attach two assemblies that aren't both in attach mode. Fixes #4147 

Fix hacky code to prime grenade by pulsing its assembly.
Removing some commented code and some duplicated proc instances.
Fixing a typo.