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
nbconvert --to script

Use extension and mime type from NB metadata
'Download as' script
Update docs about kernel_info_reply
Fix asyncy nbconvert to download
update payloads for msg spec 5

- remove auto_rewrite_input
- remove doctest_mode
- remove exit key from ask_exit
- rename 'edit_magic' to 'edit'
- remove screen_lines from page

remaining payloads ('edit', 'ask_exit', 'set_next_input', 'page')
are documented as deprecated in the msg spec
Add the . into file_extension
Missed a couple of dots
DEV: Add various events.
Merge pull request #6668 from Carreau/actions

Add notion of action to keyboard manager.
Fix input transformer bug when pasting ipython promts.

Fixes a SyntaxError that arose when pasting code containing the IPython
continuation prompt without preceding spaces, eg.:

In [1]: if True:
...:     print "No spaces before the '...:' prompt."

This issue was brought up in
"http://stackoverflow.com/questions/26297356/how-can-i-paste-the-ipython-output-in-ipython#comment41270724_26297356"

This commit adds a test for the bug, and fixes the regular expression
that strips continuation prompts.
Fixed whitespace bug when pasting IPython continuation prompt.

Fixes a SyntaxError that arose when pasting code containing the IPython
continuation prompt without a trailing white space, such as:

In[1]: if True:
   ...:    print "No space after ':' on next line."
   ...:

This might arise if the user only copies up to the end of the last
prompt, without copying the trailing whitespace.

This commit adds a regression test and fixes the regular expression that
strips continuation prompts, making the whitespace optional.
Fixed error in comments of test for inputtransformer.

The second-to-last commit incorrectly referenced issue 6674 in a comment
to a unit test.
Merge pull request #7015 from pbugnion/master

Fix input transformer bug when pasting ipython promts (issue #6674).
DEV: Pass current cell to the execute cell event.
Merge pull request #7010 from quantopian/add-events

Add various events useful for third party integrations.
API docs gardening
Fix formatting in docstring