Add feature to filter extension

I found a need to be able to filter using regular expressions and also be able to choose the property that I wanted to filter on. I added 2 properties to the filter: useRegex and filterProperty. Both fields have their default values set so that the filter will continue to work in the way it does now if users don't supply different values for those fields. If useRegex is set to true then the filter supplied will be treated as a full featured regex instead of just a string. The filterProperty property can be set to the name of the property to filter on. The chosen property can be a fancytree property or a top level user defined property. I have updated the demo to reflect the new properties and I am also willing to update the WiKi if the change is accepted.