ENT-14692: Added modular interface for event types

[victormlg]

All event types are mutually exclusive:

# this is valid

body when file_deleted(file)
{
  file_deleted => "$(file)";
}

# this is not:

body when file_deleted(file)
{
  file_deleted => "$(file)";
  file_modified => "$(file)";
}

new interval attribute

body when file_deleted(file)
{
  file_deleted => "$(file)";
  interval => 30; # waits 30 seconds between polls
}

event types that need several values, expect a set of attributes

body when file_exceeds_1GB(file)
{
  file_size_exceeds => "$(file)";
  size_threshold => "1G";
}

[larsewi]

The first commit mixes refactors, API changes, behavior changes and a new interval attribute. Please split it into one commit per change.

[larsewi]

Some nits

[victormlg]

@cf-bottom jenkins, please :)

[cf-bottom]

Sure, I triggered a build:

Jenkins: https://ci.cfengine.com/job/pr-pipeline/14813/

Packages: http://buildcache.cfengine.com/packages/testing-pr/jenkins-pr-pipeline-14813/