Update plugin to works with aloha 0.20

Installation:

    Put this dirs in "aloha/plugins/extra/textcolor"
    Ex: aloha/plugins/extra/textcolor/lib/..

    put "extra/textcolor
    Ex: <script type="text/javascript" 
          src="/static/aloha/lib/aloha.js"
          data-aloha-plugins="
                        common/format,
                        extra/textcolor"></script>

Configs:
    colors: Disponibled colors name
        Ex: ['black', 'white', 'green']
    auto_add_buttons: Autoadd color buttons on FloatingMenu (default: true)


    Configs example:
    Aloha.settings.plugins.textcolor = {
        colors: [ 'white', 'red', 'blue'],
        auto_add_buttons: false
    }