Update endpoint/grandstream/gxphd/cfg$mac

Adding support for Multipurpose keys 19-24, supported by Grandstream GXP2124.

Taken directly from the Grandstream provisioning template, and added variables to match the other 18 keys.
I'm the first to admit I have zero experience programming, so I'm certain there are other things that will need to be changed for these additions to work. I'm researching, and will likely propose more changes to the repo.
Update global_template_data.json

added yealink vlan variables for template to include vlan controls in template editor
Merge pull request #32 from xpedeus/patch-5

Update global_template_data.json
Merge pull request #23 from cmhecho/patch-2

Patch 2
Update $mac.cfg

Updated DND_On_Code to *78 and DND_Off_Code to *79 to match the freepbx default codes
Merge pull request #36 from o2tech/patch-1

Update $mac.cfg
VVX phones are not part of the SoundPoint IP line
Correct line counts to registration capabilities per Polycom Administrator's Guide.
Currently-used firmware 4.0.2B supports the VVX 500.  Add named entry.
Merge pull request #37 from wolrah/master

Polycom JSON tweaks - Add VVX 500, corrections for current models.
Merge pull request #144 from tm1000/master

Sync