Add new side panel for table filtering

[kamilfb]

This enhancement builts on top of #69, adding a side panel for viewing, editing and adding new table filters. There is a little bit more I'd like to add but sharing an early version to get your feedback. I will add a few screenshots once I figure out how to attach them here.

[kamilfb]

Below are revised screenshots.

Here is a view without any filters ("Filters" box on the left):

Adding a new filter (after pressing the big "+" button; selecting a column using a dropdown):

Showing active filters:

Editing an existing filter:

Disabling a filter:

Keen to hear your thoughts!