Added text boxes to edit the initial conditions in the GUI.

[moorepants]

Partially fixes #206.

• There are no merge conflicts.
• If there is a related issue, a reference to that issue is in the
  commit message.
• Unit tests have been added for the new feature.
• The PR passes tests both locally (run nosetests) and on Travis CI.
• All public methods and classes have docstrings. (We use the numpydoc
  format.)
• An explanation has been added to the online documentation. (docs
  directory)
• The code follows PEP8 guidelines. (use a linter, e.g.
  pylint, to check your code)
• The new feature is documented in the Release
  Notes.
• The code is backwards compatible. (All public methods/classes must
  follow deprecation cycles.)
• All reviewer comments have been addressed.

[moorepants]

@pydy/pydy-developers Review needed.

[oliverlee]

Can you add a short description of new feature to the release notes?

[moorepants]

Note is added. I don't think we need to update the online docs yet. There will be some more gui changes.

[mvnnn]

Need to space between two column.

[moorepants]

It looks like you are using chrome on linux. Can you report your browser and version?

The screenshot I have above works for Firefox 44 on ubuntu.

Thanks for trying this out.

[mvnnn]

you are right. my browser is chrome and OS is Linux mint.

[oliverlee]

Same issue with me.
OSX 10.11.3 and Chrome 49.0.2623.75 (64-bit).

[oliverlee]

You should also change the initial condition labels so they aren't displayed as functions of time.

[moorepants]

I've reported the overlap issue upstream: jupyter-widgets/ipywidgets#412. Let's see what they have to say.

[moorepants]

I've improved the display of the input boxes. My solution is hacky but it seems to work ok.

Firefox 44, Ubuntu 15.10:

[moorepants]

Chromium has some odd vertical lines beside the mathjax.

[oliverlee]

Looks okay in Chrome for OSX:

[moorepants]

Ok. I'm happy with this if you all are. I don't plan to add any more changes unless you all request. Please review and merge at will.

[oliverlee]

+1 Merge when CI is complete.