Add more validation to process

[antho1404]

Current processes still lack a few validations. Right now most of the check is done during the runtime and these checks could be delegated at the creation/compilation.

Some check to add in the Validate function

• Basic struct validation
• Directed tree
• Contains exactly one trigger
• References in map link to an existing node
• References in map link to an ancestor node only
• References should map only a task node or a direct parent
• Type mapping between output/inputs of maps/tasks
• Filter should filter valid data
• eventKey or taskKey are defined by the service