Fixed bug#8494 - Added button and keyboard shortcut in CKEditor to split quotes.

Squashed commit of the following:

commit 2e4e5fbb5d44db91ff1d93848c208f47a5e133a2
Merge: da014f8 0ed1056
Author: Marc Nilius <marc.nilius@otrs.com>
Date:   Mon May 12 11:08:17 2014 +0200

    Merge branch 'master' into bug-8494-mn-master

commit da014f80aee560f2382e60f93e4226d60fbb620b
Author: Marc A. Bonsels <marc.bonsels@otrs.com>
Date:   Mon May 12 11:03:39 2014 +0200

    Updated images; added non-retina icon.

commit 034db711cbf42b066c7c1dda5aec3cf80cc4fea7
Author: Marc Nilius <marc.nilius@otrs.com>
Date:   Mon May 12 11:02:32 2014 +0200

    Fixed typo.

commit 4de9ecbe35a4173057c54c0d0ec1f64c97d57bab
Author: Marc Nilius <marc.nilius@otrs.com>
Date:   Mon May 12 11:01:28 2014 +0200

    Prepared plugin for HiDPI icon.

commit be6c8812b3bd40a47826d00100830263b7889300
Author: Marc A. Bonsels <marc.bonsels@otrs.com>
Date:   Thu May 8 10:17:46 2014 +0200

    Added icon for splitquote.

commit efb642760603f44dca9b588afda9eefd7b8cc52b
Author: Marc Nilius <marc.nilius@otrs.com>
Date:   Tue May 6 02:47:45 2014 +0200

    Made text in plugin translatable.

commit 8a03e72adf66db8643021479c19bcf429d3ac7e1
Author: Marc Nilius <marc.nilius@otrs.com>
Date:   Tue May 6 00:14:14 2014 +0200

    Added more functionality.

commit cae5e3378b39e54a170504c9749d77ccb9782f47
Author: Marc Nilius <marc.nilius@otrs.com>
Date:   Mon May 5 16:06:30 2014 +0200

    First step for split quote plugin.