Implement rules registry

[samirketema]

• GET /api/rules
  • retrieve all rules in the rules registry
• GET /api/rules/{name}
  • retrieve rule with key of name in rules registry
• POST /api/rules
  • create a new rule, add to the rules registry
  • if this rule already exists, replace it
• PUT /api/rules/{name}
  • update a known rule

[samirketema]

Tests to start with:

• Add rule successfully
• Test nested rules
• Test badly formed rule
• Test validation with no rules
• Add a rule that has an unknown operator (this should not be allowed)
• Test updating of a rule
• Test POSTing a new rule with name clash (replace rule or reduce)