This commit brings several changes:
- Add a footprint preview pane to the eeschema component selector
- Upgrade component list to wxTreeListCtrl
- Factor out wxTreeListCtrl subclass TWO_COLUMN_TREE_LIST which
patches a column size bug
- Linkify datasheet URL in info pane
The new (eeschema, so far) hotkeys editor uses the right-click menu for the
reset command, so the reset-to-default function that was added in 6652
(git:0cd7476) was not accessible from eeschema.