MDL-40347 grade/report/grader: Fixes: Grade report does not highlight some cells properly.

Squashed commit of the following:

commit 2c2164a7e27bd2b81102251420892386e39edecc
Author: Mary Evans <lazydaisy@visible-expression.co.uk>
Date:   Tue Aug 20 12:59:47 2013 +0100

    MDL-40347 theme: Modified upgrade.txt and created bootstrapbase/upgrade.txt.

commit 4449975a0f9249785ed152f63786bf7974c1776e
Author: Mary Evans <lazydaisy@visible-expression.co.uk>
Date:   Tue Aug 13 18:42:20 2013 +0100

    MDL-40347 grade/report/grader: added RTL css previously in bootstrapbase/less/moodle/grade.less to styles.css

commit b0af8f05a411b3dbb1d9c162a0d65c7f9c069c0f
Author: Mary Evans <lazydaisy@visible-expression.co.uk>
Date:   Tue Aug 13 12:42:02 2013 +0100

    MDL-40347_M26 grade/report/grader: cleaned up grade/report/grader/styles.css.

commit 52627137dc662d47cbfdf023d056baf102f29d8a
Author: Mary Evans <lazydaisy@visible-expression.co.uk>
Date:   Sat Jul 6 17:15:12 2013 +0100

    MDL-40347 grade/report/grader: Grade report does not highlight some cells properly.

    Merged/squashed original commit by Marina Glancy who:
    - added class 'i123' to each cell in the column
    - changed JS to highlight the cells with this class instead that cells with the column number
    - changed grade report css so the .vmarked and .hmarked classes have higher priority for all rows
    - made cells in 'average range' row td instead of th
    - little corrections to css: removed background image for some cells with .header css class
    - MyMobile theme disabled cells highlighting, make sure it disables it in all cases

    Merged/squashed original commit Mary Evans who:
    - removed theme/bootstrapbase/less/moodle/grade.less
    - removed @import "moodle/grade"; from bootstrapbase/less/moodle.less
    - removed reference to plugins_exclude_sheets for grader in both bootstrapbase/config.php and clean themes/config.php
    - commented out .hidden from bootstrapbase/less/bootstrap/responsive_utilities.less
    - made minor changes to grader/style.css
MDL-40347 grade/report/grader: cleaned up grade/report/grader/styles.css.
MDL-40347 Corrections to upgrade text