Allow numeric, boolean, undefined, function? values in angular-swellrt

[atfornes]

SwellRT only stores maps, arrays, strings, and rich text objects.

However, we could use the string storage to store boolean, numeric undefined and even functions by starting the string with a pattern that should be scaped if it really mean to be in an string value. for instance using an string of the form #BOOLEAN_TYPE:true for true value.