* added VideoInfo(AbstractVideoInfo) constructor, to support later implementation for reusing info scraped into VideoPreviewInfo, into VideoInfo
* Made the Extractor class behave as a per-video object;
- most method return values are video-specific, so it makes sense (to me) to have Extractor be stateful.
- The only stateless methods are getVideoUrl(), getVideoId() and loadDecryptionCode(String)
* Implemented a constructor for YoutubeExtractor, which performs all initialisation work
* renamed VideoInfoItem to VideoPreviewInfo
* moved streaming service-related classes into their own, new package services
* added javadoc to some classes and methods (where functionality is known well enough to explain)
* De-duplicated common fields between VideoInfo and VideoPreviewInfo by moving them into a common superclass: AbstractVideoInfo
* Removed 2 methods which only call super(), and therefore are unnecessary: PlayVideoActivity.onResume() and PlayVideoActivity.onPostCreate(Bundle)
* still need to use the start position value stored in the PlayVideoActivity's Intent bundle, to set the VideoView using seekTo()
* need to test timestamp extraction regex, and possibly move it somewhere else
*need to find a better way to get the startPosition value to ActionBarHandler, which I thought used VideoInfo objects, but apparently doesn't
* currently there is a small setStartPosition() method
-replaced single use of terrible_unescape_workaround_fuck(String) with call to URLDecoder.decode(String, String)
* tested new regex implementation of YoutubeExtractor.getVideoId(String)
- deleted old HashMap-based implementation of YoutubeExtractor.getVideoId(String)
* Miscellaneous typo corrections
* replaced direct page-scraping extraction of video publication date in YoutubeExtractor.getVideoInfo(String) with jsoup-based scrape of <meta> tag field in YYYY-MM-DD format
*similarly, replaced direct page-scraping extraction of view count with <meta> tag field.
Both <meta> tag fields still need to be formatted locale-specifically
