Colours

[tduva]

• Changed some colours so they are more easily distuingished. These work better for myself, but I don't know how it would be for others with different or more severe colorblindness (or screens, or whatever). Either way, it should hopefully be better.
• Added a symbol to each colour, toggleable in the options.
• I re-added the original hover effect (changing colour brightness) since the other options didn't really seem that nice. Since this would mostly affect the player while changing colours (viewers would mostly just have to recognize non-hovered colours), the symbols can be enabled if distuingishing colours is an issue.
• Added keycodes for 0-6 on the NumPad, which could be useful.

Edit: I didn't rename the CSS classes for the changed colours since I wasn't sure what to call the colours or whether they are even final. Not sure if it would be better to rename them to something neutral like "colour1" rather than the actual colours. Idk.

[rybak]

It seems that lightning.png isn't used, so it could be removed.