Add per-form validators to services markup.

This allows to implement joint validator for hostname template and number
of instances in all services.

Also:

1) Refactor append_properties function(rename to push_properties
and move to field classes).
2) Change service forms markup so each form has a name.
3) Change yaql-validators syntax to {YAQL: validatorExpression}.

Change-Id: Ia6b32e14213b147881b242710ca130a4dea3cdb2