Add Load and Activate Real Time Commands to SeqN

[goetzrrGit]

Summary
Added immediate_activate and immediate_load to SeqN.

@IMMEDIATE
ECHO "" 
@LOAD("seqA")

SeqJson

{
  "id": "SeqC",
  "metadata": {},
  "immediate_commands": [
    {
      "args": [
        {
          "type": "string",
          "value": "",
          "name": "echo_string"
        }
      ],
      "stem": "ECHO",
      "type": "command"
    },
    {
      "args": [],
      "sequence": "seqA",
      "type": "load"
    }
  ]
}

[joswig]

Test cases and functionality are good.

My comment on the seq-json types is because distinct literal values help with control flow analysis. It also feels like we have a lot of type assertions.