Remove unused function itype::is_covering

This is handled by the item class directly (items can have differently sided coverage, differing from the coverage of the it_armor type).
minor fix to fix in filename logic
shorten filename length, was not included in prior fix
Initial survivor's arsenal update
Json eror
More json fixes
Even more json fixes. Going to fix my compiler after these
Remove the prompt for foraging

I can't think of a reason why you'd particularly not want to forage, and it makes wilderness scavenging much less tedious.
Remove unused parameter

And if I'm reading things correctly, interrupting the activity should be handled in the activity handling code and not here, correct?
Remove unused function item::is_other()
Move the static null-item type into the nullitem function.

Make the function static and visible only to the item class, nobody needs to know this implementation detail.
Also make the null-itype a static object, not a pointer.
This makes sure the memory is cleaned when the game closes, but never before.
Improve is_null check by comparing to the static null-item pointer before checking the actual type id.
Move access to it_armor::storage into a function of item class
Move access to it_armor::encumber into a function of item class
Move access to it_armor::coverage into a function of item class
Move access to it_armor::warmth into a function of item class
Move access to it_armor::thickness into a function of item class
Move access to it_armor::env_resist into a function of item class
Move access to it_armor::is_power_armor into a function of item class
Add item::get_random_material

to move it_armor::(bash|cut)_dmg_verb out of itype, now it can be used on
the random material given by the item class. This allows to get the damage
verb without knowing the itype class.
Add item::get_base_material

To move itype::dmg_adj out of itype.h, now the damage adjective can
be retrieved from the material returned from the item object without
knowing the itype class.