TablePager: Load images via CSS backgrounds rather than HTML <img>s

Moved files from directory: skins/common/images → resources/src/mediawiki/images
and renamed:

* arrow_disabled_last_25.png  → pager-arrow-disabled-fastforward-ltr.png
* arrow_disabled_first_25.png → pager-arrow-disabled-fastforward-rtl.png
* arrow_disabled_right_25.png → pager-arrow-disabled-forward-ltr.png
* arrow_disabled_left_25.png  → pager-arrow-disabled-forward-rtl.png
* arrow_last_25.png           → pager-arrow-fastforward-ltr.png
* arrow_first_25.png          → pager-arrow-fastforward-rtl.png
* arrow_right_25.png          → pager-arrow-forward-ltr.png
* arrow_left_25.png           → pager-arrow-forward-rtl.png

The new names are not very intuitive, but there's a mostly reasonable
system behind them and we need names like this to have them
automatically flipped for RTL styles.

Bug: 69277
Change-Id: Ica34cdd5fcc9340a94fb5e60bb34c30266953dcb
IndexPager: Don't generate rel=first and rel=last

These values for the "rel" attribute (aliases for 'begin' and 'end',
respectively) have only appeared as proposals for the HTML4
specification, but were then explicitly dropped.

The story of them and more links are available on
<http://microformats.org/wiki/existing-rel-values> (search for
'first', 'last', 'begin', 'end'). The gist is that they were
intentionally dropped and therefore should not be used.

Change-Id: I33afd1364bf9ccf79c11a2a050ad0c4ff52c447a