Plural Change (straps->strap)

The bulk update request #109 has been approved by @Talulah.

rename chest_straps -> chest_strap

Self explanatory - singular denotes both single and multiple. Plural does not.

and what do you think about single strap?

That doesn't reflect specifically chest/breast straps or holster (depends on context)
I'm not referring to strap vs straps in general.

The bulk update request #109 (forum #832) has been approved by @Talulah.