Add ViPile for Vi-like filter navigation

Binds j and k to move within the pile.
Add ViColumns for Vi-like column navigation

Binds H and L to move between columns.
clear all filters if no checkboxes are selected, fixes issue #15
version bump to 2.0.2
Merge pull request #14 from matze/match-navigation

Match filter and column with todo navigation
updated focus keybindings

- let j k selection be handled with a command_map change on the todo ListBox
- allow tab to toggle focus between the filter panel and the toolbar
- small change to toolbar button names
added new keybindings to help and readmes, verison bump to 2.0.3
fixed bug where completing items didn't update the selected todo, changed sort keybinding back to s
version bump to 2.0.4
added solarized-dark theme, removed two unused color definitions