Closes #7.

Summary of Changes

• Filter box in the menu bar.
• Expected input has the form <scope>:<filterString>, where scope is one of module, class, function, or parameter and filterString is an arbitrary string. Each scope must occur at most once.
• The filterString must occur anywhere in the name of the declaration for it to be matched. This means module:neighbors would match sklearn.neighbors._kde, for example.
• Search is case-insensitive.
• When the class filter is active, all top-level functions are removed.
• When any filter is active, nodes in the tree view without children are removed.

Screenshots

Testing instructions

• Try the following queries and vary them:
  • module:neighbors
  • class:transformer
  • function:fit
  • parameter:y
• Check that the original view is reinstantiated when the filters are removed