Options; reworked, with fixed footer.

Changes:
   - Added caption "Miscellaneous toggles" to visually separate the
     link-hints checkbox from the others.
   - Made the text for the two link-hint character sets the same.
   - The "Show advanced options" link now spans two columns, so it does
     not affect its column's width, so the layout doesn't change when
     the options below the fold are expanded.
   - Added a fixed footer containing the help text and the save button.
   - The text of the save button now changes when it is enabled.
     (I sometimes find it hard to tell whether its been activated or
     not.)
   - Control-Enter anywhere on the page saves all options.
   - Aligned the entire options table left, instead of centered.  This
     is the chrome style.  However, it also makes it easier to get the
     alignment right between main table and the footer.
   - Change width of main wrapper such that it actually matches the
     table's width.  This aligns the right edge of the bar under the
     title with the right edge of the second column of the table.
Options; Exclusion headers, style fiddles.
Options; Ctrl-Enter blurs active element.
Options; use consistent capitalization.
Options; add help text for scrollStepSize.

No help is really needed.  However, the gap where the help text should
be looks ugly.
Options; restyle exclusion rules.
Options; release focus on clicking advanced.

When the show/hide advanced options link is clicked, it gains the focus,
and the URL is displayed by chrome in the bottom-left corder of the
window.  This partially obscures the footer, so we immediately blur the
link.

Also, same for the "show help" link.
Options; Reintroduce min-height for exclusion rules.

We need to keep *some* minimum height to avoid the help texts colliding.
Merge remote-tracking branch 'smblott-github/option-for-options-page'

Conflicts:
	pages/options.html