truncate potentially long CompositeErrors

If you have a typo in a task on 100 engines, the local exception will be a bit ridiculous.

This defaults the truncation to 4 tracebacks (could be even fewer, or even one?),
and you can set the tb_limit attribute of CompositeError to adjust this.

Prompted by [this SO question](http://stackoverflow.com/questions/14635935/silence-or-condence-ipython-parallel-exceptions).
fix celltoolbar layout on FF
fix button css
remove one useless element
get monospace pager back
exclude fabfile from tests

closes #2890
Merge pull request #2893 from minrk/fab

exclude fabfile from tests
make baseProjectUrl a method in Menubar
add option in menubar to set baseproject url
make base project url a method on notebook list
change more baseurl
Don't assume test case for %time will finish in 0 time.

Closes gh-2899
pass baseUrl as option
Merge pull request #2900 from takluyver/i2899

Don't assume test case for %time will finish in 0 time

Closes gh-2899
next release will be 1.0
catch AttributeError in cleanup_connection_files

can be triggered during garbage collection (os.remove is destroyed before the KM instance)
Revert "patch deletion in codemirror"

This reverts commit 331a5f7fe85a6e894c35b64cd7987ed53f59ea57.
monkey patch codemirror with new functionality

use marijnh recommended way:
https://github.com/marijnh/CodeMirror/pull/661
fix a few remaining KernelApp/IPKernelApp changes
update cm update instruction