flasky.css: Added font_family variables
flasky.css: Added link_color variables
flasky.css: Use percentage based font sizes

Let the header font sizes scale according to the body font size
flasky.css: Added font_size variables
theme.conf: Added css template variables as theme options

This makes it possible to modify the theme appearance without forking the
project.
theme.conf: Added link_text_decorations option
theme.conf: Added font_weight options
Merge branch 'variables'

Conflicts:
	flask/theme.conf