Advanced filter functionality

[mdenker]

as discussed in Lausanne, details to follow
-- Better syntax to specify complex search queries
-- Output of search

[JuliaSprenger]

• write filter functions, which are based on lists of neo objects rather than as function of specific neo objects (multiple filters can be applied sequentially)
• output of filter function should be list of neo objects
• filters should be able to filter based on annotations (eg. return only objects, which have a specific item in a list of an annotation)