Full styling

Complete color/attributes support!

This improves `weechat.js` with a static function `WeeChatProtocol.rawText2Rich(txt)` which may be called with raw message text `txt` to get an array of text elements with added style. We use this in `model.js` to add correct classes according to color/attribute names and overrides.

A bunch of style classes are defined in `style.css`. Prefixes stand for:

* `co`: color option
* `cw`: WeeChat color
* `ce`: extended color
* `a`: attributes

Then `f` for foreground, `b` for background and `a` for attributes.

Basic ("WeeChat") colors use [this scheme](http://color.smyck.org/) now, with a slightly darker background, which I believe gives a better result than the raw, high-saturated default terminal colors we had previously. Feel free to modify this (in `style.css`) if you don't like it.

A few minor UI improvements also in this PR, which you might not like:

* prioritize Consolas and Monaco over Inconsolata, because I'm testing on Windows and Consolas looks much better
* increase the vertical line's brightness between the prefix and the messages in buffer lines
* increase the bottom padding of the buffer lines region since the glow of the input bar falls over the text otherwise
* subtle bufferline hover background color