[MWC.Core] Add new constants in order to work with twitter API v1.1
[MWC.Core] Rename XmlFeedParserBase -> FeedParserBase because new Twitter API works with JSON
[MWC.Core] Change AuthorUrl, FormattedAuthor, RealName properties to avoid exceptions + code formatting
[MWC.iOS] Tweet info and navigation bar overlapping fix
[MWC.Core] Add changes to .csproj file
[MWC.Core] Class which is used to handle oAuth2 authentication
[MWC.Core] Update twitter parser with ability to work with JSON data sent by twitter API v1.1
[MWC.Core/iOS] Code formatting
[MWC.Core] Remove deprecated comments, add Initialize method, override AllItems property
[MWC.Core] Make AllItems property virtual
[MWC.iOS] Add not null constraint + TwitterScreen.cs code formatting