#11 Sort based on editor activity

[Snow]

I have made a few enhancements to help me find my
most-used editors more quickly.

Enhancements:

1) Pinned editors are in bold.
2) Pin button on EditorList toolbar.
3) Option to sort pinned editors to top of list.
4) Dirty editors are shown in red (except when selected
unfortunately; I can't work out how to change that).
5) Option to sort dirty editors to top of list (under
pinned ones).
6) Option to sort editors according to "Snow's Special
Ranking Algorithm". Which measures activity of editors
and tries to put the ones used the most near the top
(under pinned and dirty).
7) Option to highlight the most recently visited
editors in green.
8) The dirty flag is not used when sorting alphabetically.
9) Fix a bug to do with opening and closing the
EditorList view.

All of the new sorting options work only when
alphabetical sorting is off, and can be disabled from
the preferences page (to give current behaviour).

The list is only resorted when an editor is
pinned/unpinned; dirty status changes (edited or
saved); editor added/removed; or alpha-sort
enabled/disabled, to avoid the list changing "under the
user's feet" too much.

Unfortunately Eclipse's public API for the pin action
will only show the pin button when the "automatically
close editors" option is set. Since I want to pin
editors even when this is unset I had to use an
"internal" API.

I've been using the patched version for a couple of
months with no adverse affects so it should be
reasonably stable.

The zip file contains a patch in the root, and a
complete source tree. You don't need both, use
whichever is most convienient.

I release all additions and modifications in the
attached zip file under the EPL (Eclipse Public License).

[Snow]

Sort based on editor activity