Add schema and schema validation to CI

[amoeba]

In #136 (comment) @LtRipley36706 noted a tool they built broke when element order changed. I think it makes sense to create an XML schema for the list and perform validation on PRs.

Contributions welcome for this.

Edit: This should probably be even more through, see comments below.

[amoeba]

I misinterpreted what the original issue was. The issue wasn't element order but that the values got swapped (i.e., "software" is marked as "PvE" and "type" is marked as "ACE". Should be swapped.

So validation should be checking values too.

[amoeba]

Talking about this more with @LtRipley36706, the checking that's done in a PR could be even more thorough:

• Make sure GUID is unique
• Make sure name is unique, not found in some specified exclusion list ("ACEmulator", "Frostfell")
  emu is valid type
• emu is one of a few options (ACE, GDLE, etc)
  server host + port is a resolvable a host, and connectable
• Server host+port is online, see Add up checking to PR CI #141
• Type is valid (PvE, PvP)
• Status is one of a few options
• Website URL if provided should resolve
• Discord invite URL if provided should work (probably can just do a HEAD request on it)

[amoeba]

Basic XSD based validation in CI added in #165. More could be done here.

[amoeba]

Another good validation thing would be to verify the id is a valid GUID. See 1540264.