UI to customize Timeline design

[jeremyboggs]

Create a user interface to customize design of the timeline to better match the selected public theme. Make this global for all timelines, and modifiable for specific timelines.

Properties to customize:

• Height of timeline (in px)
• Top band color (color picker)
• Bottom band color (color picker)
• Top band interval (select)
• Bottom band interval (select)
• item icon (select, reads dir in theme-name/neatline-time/images/icons and plugins/NeatlineTime/views/shared/images/icons)

[jeremyboggs]

Updating this to add ability to edit timeline design on a per-timeline basis. Should be easy enough to implement for each by adding an options column to the NeatlineTimeTimeline model, which we need to do anyway to store other options.

[jeremyboggs]

Updates ticket to add list of properties to make customizable.

[erochest]

I like this, but with everything else going into this, maybe we need to just have a hook for a CSS file, similar to what Neatline does. We'll also need some way to limit the scope of the css.