Makes the MinimapView working on a given PaneView

It’s a preparation in order to have one minimap per pane.
Removes right: 0 that prevent left pane minimap from being visible

Pane views aren’t relative so when setting `right: 0` the
minimap is moved to the extreme right of the editor.
It appears that without this rule the minimap is still positioned on
the right but of the pane view this time.
Adds handler for multipane minimaps

Instead of retrieving the `activePaneView` we use the `eachPaneView`
method to creates a minimap for every
pane view present and future.
Adds defensive test on editor	 in the immediate callback of update routine

Due to racing conditions during the `destroyed` event dispatch the
editor can be null, until a better solution is implemented it will
prevent the delayed code from raising an error.
Merge pull request #12 from abe33/feature_minimap_per_pane_view

Implements one minimap per pane view