Implement all (undocumented) forms template insertion tags

[n2ygk]

In #330 several GPS-related missing insertion tags were identified and implemented. In the process of researching those tags at least one other tag was noticed, but there are probably more. This will require scanning all the Winlink form templates for tags that are not currently being substituted and deciding if it's even worth bothering implementing them.

The tag identified so far is:

• InternetAvailable: Referenced (but never used) in GENERAL Forms/Winlink_Check_In_Initial.html and GENERAL Forms/Winlink_Check_out_Initial.html

While there is existing Winlink documentation of insertion tags, it is incomplete.