Move zone set/get properties to own source file

Move zone set/get properties to own source file

In order to make zone.c more readable, we are splitting it up in
separate source files. This moves the set and get functions to its
own file ("zoneproperties.c").

Since this code accesses the zone structure directly, move the
'struct dns_zone' and its prerequisites to "zone_p.h".

The helper functions 'inline_raw()', 'inline_secure()',
'dns_zone_setview_helper()', 'zone_settimer(), 'set_resigntime()', and
'zone_freedbargs()' need to be internally accessible to both source
files.

A few set/get functions remain in zone.c for now:
- dns_zone_getserial
- dns_zone_getversion
- dns_zone_setviewcommit
- dns_zone_setviewrevert
- dns_zone_get_rpz_num
- dns_zone_set_parentcatz
- dns_zone_get_parentcatz
- dns_zone_setrawdata
- dns_zone_setskr
- dns_zone_getskrbundle
- dns_zone_setnsec3param
- dns_zone_setoption
- dns_zone_getoptions
- dns_zone_getrequesttransporttype
- dns_zone_getredirecttype
- dns__zone_getnotifyctx
- dns_zone_getgluecachestats
- dns_zone_setplugins
- dns_zone_setserial
- dns_zone_getxfr
- dns_zone_getkeystores