Show the character count correctly for a tweet

[dalmaer]

As long as the setting is true (e.g. make sure to add a default setting and check for it) show the character count information.

This involves:

• Limit to 140 characters
• Light grey early on (first chars)
• Get darker as more chars are typed
• Turn yellow when 50 chars left and get more orange
• Turn red when negative

[ewpreston]

May want to improve the gradient calculation