Adding specific class names to buttons in posting_buttons.html

Until now every button of the posting-editor has a standard "class" name "button2".

If you try to use a extention or simple css code you have to add a new class tot the button, for example:

Bold-Button:
class="button2 bbcode-b"

Now you're able design the button with custom styles.

I think we should add at standard conditions a special class to those buttons and for custom buttons simply grab the "value" of the button.

Example:
Bold => bbcode-b
Italic => bbcode-i
Underline => bbcode-u

In css not allowed signs like "=" has to be replace by "-" or something similar. Because "input.list=" won't work, but "input.list-" does.