remove raw cell placeholder on focus, closes #5238
update notebook quickhelp on new shortcuts
removing keyboard shortcuts should also update help
rebuild.QuickHelp event sets the dirty bit

QuickHelp is rebuilt on show if the dirty bit was set.
remove recreation of QuickHelp
first pass at capitalizing keyboard shortcuts
prettify combo keyboard shortcuts
fix capitalization of mode-switching keys
DRY: style in one place, removed code duplication
fix raw_input CSS

I had to express padding in px, not em for consistent appearance.
I'm not sure why.
semantic names for indicator icons

For all of the discussion that we had about what kind of icons should
and should not be used to indicate what mode the notebook is in, we
never went through to make it possible to override it.

With this change, it is now possible to override what icons are
displayed for Command and Edit Modes.

For example, @minrk liked the fighter-jet icon for Command Mode, so he
can put this in his custom.css

.ipython-command-mode:before {
     content: "\f0fb";
}
semantic names for kernel status indicator
ensure ipython-command-mode icon displayed on load
better fix for starting with Command Mode icon
give hint on where to find custom.js
fix ambiguous raw_input classes
simplify raw_input css

for once, vertical-align: baseline is the right choice
fallback on copy, copyfile if copy2 fails

in notebook manager
remove some redundant font-family: monospace

`pre`, `code` tags already set the font-family in these contexts.
Setting it again in the surrounding context is redundant,
and causes inconsistency when embedding notebooks in HTML
(e.g. nbviewer).
do not install less sources

only their css build results are used after install