Remove HTML tags from translations + add plural forms

The following lines in /src/youtube/scope/query.cpp add HTML codes to the translations:

    string videos_count = "<b> "+ format_fixed(channel->video_count()) + _("</b> videos");
    string views_count = "<b> "+ format_fixed(channel->view_count()) + _("</b> views");
    string subscribers_count = "<b> "+ format_fixed(channel->subscriber_count()) + _("</b> subscribers");

This is error prone and can break the HTML with translation errors. Also, translators can't use proper plural forms with these strings. I recommend fetching the translations with the following method:

ngettext("%d video", "%d videos", channel->video_count())

and then replacing %d in the result with "<b>" + format_fixed(channel->video_count()) + "</b>"