Powerful filter functions for Neo

[mdenker]

The user is able to flexibly select data from Neo objects, filtering them by object type, annotation, etc.

Issues to be addressed in the epic:

• current filter function has a difficult syntax, no/bad documentation
• implement multi-filtering -> Filter an object, and then apply another filter
• multiple allowed values: AND’s and OR’s of annotations, combining queries
• exclude values: extract objects that do not have a certain attribute
• support for regular expressions?
• multi annotations –> For AnalogSignal objects, one annotation for each signal in the object. For Events and Epochs, one annotation for each event/epoch.
• Should recognize quantities –> search for something like T_min==1000ms.
• Masking of data within a data object (Note: Robin G found an interesting way to do this)