Add notion of action that differs from  shortcuts.

This decouple the notion of shortcut from the notion of executed "action"
This allow the shortcuts manager to be purely describe as data, and the
same action to be later refered to either from the shortcut, from a toolbar
button or a menu.

This also implement a more complete keyboard shortcut handler which is
able ton interpete sequences like `Cmd-X,Meta-v` By storing the
shortcuts in a tree.
remove debug
add test warning shadow
Tooltip on toggle button
Make favicon and logo images blocks in the template
[issue3992] set/get use cases for 'env' and new 'set_env' magic
don't execute if kernel is not connected
Don't pass IPython-specific args to non-IPython kernels

add a few FIXME notes that the IPython-kernel special treatment
will probably want to be removed in the Jupyter explosion.
Allow run_line_magic to be called from scripts

Don't blow up if looking back up the stack trace fails.

Reported on rpy2: https://bitbucket.org/lgautier/rpy2/issue/184
/valueerror-call-stack-is-not-deep-enough
Merge pull request #6959 from minrk/check-kernel-execute

don't execute if kernel is not connected
Actually typeset latex
Merge pull request #6965 from takluyver/var-expand-locals-softfail

Allow run_line_magic to be called from scripts
Merge pull request #6953 from mattvonrocketstein/issue3992

[issue3992] set/get use cases for 'env' and new 'set_env' magic
Merge pull request #6923 from SylvainCorlay/toggle_button_tooltip

Tooltip on toggle button
Public server firewall configuration

Added section on firewall configuration.  This should prevent users (like me) from struggling
to figure out why their servers aren't executing code.
Merge pull request #6881 from jasongrout/template-blocks

Make favicon and logo images blocks in the template
Fixed port range

Actual port range for ZMQ is 49152 through 65535.  Also fixed some grammar/spelling issues.
Add debugging print for test failure on Windows
Merge pull request #6970 from takluyver/win-envvar-not-str

Add debugging print for test failure on Windows
More info about erroneous environment variable