YoutubePlaylistIE: get *all* videos

For that, we add parameter safeSearch=none that asks youtube not filter
results before sending them to us.

Note: this parameter could be added to YoutubeSearchIE and YoutubeUserIE
as well, but I don't know what would be the impact in term of unwanted
results. Maybe expose that as a parameter? For a playlist it's different
since the user chose what she put in the playlist.
Merge pull request #887 from anisse/master

Fetch all entries that are in a youtube playlist

Also add a test.
Ignore invalid dates (Fixes #894)
SteamIE: only verify the age if needed

Also use the _html_search_regex function
Revert "Fix GooglePlusIE: the video_page url has changed of place"

The old method is working again.

This reverts commit 449d5c910cefdbfdfc5aa13d682dc46988a5318e.
Update the TumblrIE: the video is no longer available
DailymotionIE: fix the extraction of the video uploader and use _search_regex for getting it
RBMARadioIE: fix the extraction of the JSON data
TEDIE: download the best quality video and use the new _search_regex functions

Also extracts the description.
Show which IEs are slow during release
release 2013.06.21
Leave out sig if not present (#896)