Shut down kernels in parallel

When stopping the notebook server, it currently sends a shutdown request
to each kernel and then waits for the process to finish. This can be slow if
you have several kernels running. This makes it issues all the shutdown
requests before waiting on the processes, so shutdown happens in
parallel.

KernelManager (and MultiKernelManager) gain three new public API methods
to allow this:

* request_shutdown (promoted from a private method)
* wait_shutdown (refactored out of shutdown_kernel)
* cleanup (refactored out of shutdown_kernel)
Simplify KernelManager.cleanup()
Expose keyword arguments of KernelManager methods on MultiKernelManager
Rename wait_shutdown to finish_shutdown
When a preset is activated fire "preset_activated" event.
On "preset_activated" event, update the value of the maintoolbar select element that lists celltoolbar presets.
When a preset is registered after notebook is loaded, active it if needed.
Make sure that celltoolbars are hidden
when a notebook without "celltoolbar" entry in metadata is loaded.
update CodeMirror to 3.24

to be backported to 2.1
Fixed example to work with python3

Just some print parentheses added.
Make rmagic display call compatible with updated API

Passing all arguments as keywords will work with the previous API as
well.

CC @davclark - You'll want to copy this change across to rpy2, because
without it, rmagic is broken with IPython master.
Merge pull request #5832 from Zaharid/ip3fix

Fixed example to work with python3
Merge pull request #5834 from takluyver/rmagic-display-fix

Make rmagic display call compatible with updated API
fix typo in v2 convert

resulted in NameError on orig_version because arg name is from_version
pass on install docs

there were many False statements, and no-longer appropriate recommendations to use easy_install.
Merge pull request #5837 from minrk/install-doc

pass on install docs
Close graphics dev in finally clause\ncloses #4408 (already closed)
Merge pull request #5839 from davclark/rmagic-graphics

Close graphics dev in finally clause
Add failing test for issue 2412

Writing history to a file including output fails
Fix writing history with output to a file in Python 2

Closes gh-2412
fix typo in nbconvert help

Latex template is 'base', not 'basic'
cf. https://github.com/ipython/ipython/tree/master/IPython/nbconvert/templates/latex
remove Firefox-specific CSS workaround

The bug being worked around appears to be fixed either in CodeMirror or Firefox (tested with FF 29).

Importantly, the workaround appears to *introduce* incorrect behavior

closes #5192
closes #5364