Allow collection size constraint

Allow to define collection size constraint via data attribute on the field
- data-constrained-collection-min-size
- data-constrained-collection-max-size

if min size is defined, then, at initialization, at least [min size items] are create (if not already existing)
if max size is defined, it is not possible to add more items when max size is reached

New events fired on this._container:
- prototype.maxsize-reached (when the last permitted item is added)
- prototype.maxsize-already-reached (when addField is called but the maximum size has already been reached)