Proposed Fix for Issue #69 - Better handling of Always-On-Top apps

[bradrhodes]

See Issue #69 for a description of the issue.

This adds the ability to Pin items to the bottom of the list so that they won't appear on the top. This can be done via right-click context menu or via keyboard shortcut (Ctrl+L in order to keep with the suggestion of having more Vim-like keybindings proposed by trond-snekvik.

The implementation is basically to maintain an in-memory list of windows that ar pinned. When the list is sorted, those items are moved to the bottom. This is not persisted between sessions because it's difficult to describe which windows from multi-window apps should be pinned. For example, if you pin a Chrome window, once you restart, how do you know if a new Chrome window should be pinned or not?

[bradrhodes]

After using this for a couple of weeks, it's not a perfect solution. I run Google Hangouts as an Always-on-top app. Pinning to the bottom works fine, however when new child windows are spawned, it seems to change the hWnd Id of the window so it will end up on top again.

In practicality, this isn't a huge deal as it is simple to just pin it again but perhaps there is another method that could be better.