Remove atom-space-pen-views and custom elements registration

Not all themes seem to have this problem.

Since there is no input above

Return no icons for tabs, same defaults as fuzzy-finder et al for MRU
UX items.

Remove unnecessary onWillDeactivate method from file-icons service

Account for dropping in another pane container

Fix drop marker position

Destroy tabs when the pane is destroyed

Automatically scroll to tab if not completely visible when activating a pane item

This reverts commit acbbe10b2947fef1f455e1e7c281683970c5c390.

Fixes #362

Fix invalid reference to item field and remove unused variables

Use package's name to identify context of icon-service

Don’t assume lastCoords is defined in drag end handler

Read pane/item directly off tab element instead of looking up via DOM

Determining a tab’s pane or item via the DOM is unnecessary because we
store this state directly...

Switch styling to preserve whitespace in file names

Resize tabs when mouse moves away from tab bar (updated)

Ignore addNewTabsAtEnd config when dragging to a different pane

Changed one line of logic so that dragging a tab to a different pane doesn't trigger addNewTabsA...

Wrote a test that requires that a tab to be allowed at any target index when being dragged to a ...

Drag and drop layout management

remove needless prefixes

Make close all tabs work without a tab focused