Bug 972061 - Update style of Sync intro and manage pages r=ttaubert

From ff216e4d7d2c5957c09ba03028b0fec76303ab30 Mon Sep 17 00:00:00 2001
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 .../base/content/aboutaccounts/aboutaccounts.css   |  36 --
 .../base/content/aboutaccounts/aboutaccounts.xhtml |   8 +-
 .../aboutaccounts/images/graphic_sync_intro.png    | Bin 5566 -> 9304 bytes
 .../aboutaccounts/images/graphic_sync_intro@2x.png | Bin 10764 -> 19655 bytes
 browser/base/content/aboutaccounts/main.css        | 380 ++++-----------------
 5 files changed, 76 insertions(+), 348 deletions(-)