Add support in WebUI for configuring boot ordering

[digimer]

@ylei-tsubame boot/shutdown ordering is complete. To configure this in the WebUI, update the database this way;

• To configure X boots after Y, set server_start_after_server_uuid to the UUID of the server that needs to boot first. Set server_start_delay to the number of seconds, with the default being 30.
• To mark a server as "stay off", we need to create a variables entry;
  ** variable_name = server::<server_name>::stay-off
  ** variable_value = 0|1 (0 is boot, 1 is "stay off")
  ** variable_section = servers
  ** variable_source_table = servers
  ** variable_source_uuid = servers -> server_uuid (this is how we'll prevent collisions with two nodes with matching names)
  ** variable_description = striker_0001

Put this configuration in the server config page;