[Engine-Twitter] Implemented /retweet command (closes: #480)
Engine(-Twitter): Refactored newline normalization into MessageBuilder
Engine(-Tests): recursive html parsing used same TextMessagePartModel in multiple places

when setting the text of a specific TextMessagePartModel, the text somewhere else in the message also changed
now there are unit tests checking for such behavior
Engine: erasing newlines caused words to be stuck together

reintroduced newline converter from FeedMessageBuilder
Common: Added RSS feed parser
Common: Changed namespace of RSSFeed
Common: Fixed LastBuildDate DateTime parsing bug in RSSFeed
Engine-Feed: Initial Commit