Add support for Fira Code progress bars

Add FiraCodeProgressBar option that enables Fira Code progress bars as seen in Fira Code's GitHub repo. Enabling FiraCodeProgressBar will use the Unicode range U+EE00-U+EE05 (from the Private Use Area Unicode block) for rendering progress bars, which is what Fira Code uses.

Since it probably does not make sense to enable both FiraCodeProgressBar and ILoveCandy at the same time, only ILoveCandy will affect progress bars if both options get enabled at the same time.