Change radius of radial timelines

[mattbrehmer]

(alternative to issue #36)

The radius is currently adjusted automatically given the window/main_svg dimensions, the number of tracks, (and the number of facet or segment columns in the case of faceted / segmented layouts).

The radius could be manipulated directly by clicking and dragging on a control point at the center of a radial timeline. Changing the radius of a single facet should update all facets in sync. This will in turn affect the number of facet rows and columns.

A global minimum and maximum radius would need to be specified based upon the resolution.

[mattbrehmer]