A pipe function to aid collections filtering

[PK1A]

While rendering collections of data a common scenario is to provide possibility to filter a collection (limit it to records matching certain criteria). It is convenient to write something along those lines:

 {foreach itemIdx, item in ctrl.tableItems | filter:criteria}...{/foreach}

There are many ways of expressing filtering criteria, one could think of:

• a string / RegExp that is used to match items
• a function, similar to the one used in Array.prototype.filter

In any case it would be convenient to have such a helper in the framework as the case for filtering is very common. It would be also go hand-in-hand with the ordering helper already built-in.

[PK1A]

This is somehow linked to #239 as we need to be able to read the size of a filtered collection.