Minor toolshed fixes / tweaks

[ElectroJr]

• Ensures that IConError messages don't use markup when they are meant to be using plain text
  • This was preventing toolshed from printing error messages when using array types, as [] is invalid markup.
• Makes GetParserForType() always cache the returned parser.
  • Currently generating the completion suggestions for something like val EntityUid[] is really slow because it would constantly try to use reflection to recursively get non-existent parsers for all the array interfaces.
  • I'm not sure why it wasn't always being cached before, I assume it was unintentional?
• Caches the TypeTypeParser completion options