Header improvements and dynamic theming

[Splaktar]

In PR #36 @tasomaniac mentioned that I/O Extended had a custom color theme in the Frisbee app.

Previously Firefly had some custom color theming for some of the different events like WTM and Android (while most event types did not have custom colors). During the initial version of the angular-material implementation, this custom coloring was removed from Firefly.

This isn't too hard to do with angular-material's theming system, but there are some details that need to be worked out around how the dynamic site URL + dynamic theming can work together.

Another issue is that the boomerang + GDG Events image in the toolbar is black. Ideally the boomerang would be an SVG and the 'GDG Events' portion would be text. This would allow angular-material to change the color of the text (between black and white) to work with the color of the toolbar automatically.