Implements one minimap per pane view

This is a work in progress, but I open the PR to starts the discussion.

Basically the `MinimapView` now takes a `PaneView` in its constructor. The `minimap` module will plug onto `eachPaneView` and create a minimap view per pane. The minimap registers to the `destroyed` event of the pane item and destroy itself at that time. 

For the moment, the only changes in stylesheet is the deletion of the `right: 0` rule on the minimap view, it prevent minimaps for left panes to appear behind the right panes.

There's a lot of testing to be done to make sure that all cases are properly handled and probably more refactoring but it seems that the feature is pretty stable as it is, I just have an issue when creating a new pane, the minimap doesn't have the syntax highlight until a new view is activated in the same pane.