plugins.tv4play: Add SWF verification to the HDS streams.

This only seems needed on encrypted streams, which we can't
play anyway, but at least we now give a sane error.
plugins.dailymotion: Refactor to use the validation API.

Also added support for mature videos and alternative servers.
Replace CLI with "command-line utility" where possible.

Sounds more fluid IMO.
plugin.api.utils: Add parse_query.
plugins.youtube: Use plugin.api.utils.parse_query.
plugins.picarto: Minor tweaks.
plugins.justintv_common: Use plugin.api.utils.parse_query.
plugins.weeb: Use plugin.api.utils.parse_query.