NeoTree, Upgrade, Version, Scala, Themes, Banners, Fixes and Tweaks

• Revamped NeoTree for a slick lightweight filetree browsing experience. See documentation for details on how to use the new NeoTree.
• Version of Spacemacs in now displayed in the startup buffer. The version can be echoed at any time with function spacemacs/display-and-copy-version.
• New button on the Spacemacs startup buffer: Update Spacemacs. For now it only updates the ELPA packages (thanks to ralesi)
• Lots of tweaks for scala layer. Add support for flycheck linting, better ensime integration (thanks to chrisbarrett)
• Add support for hi2 in haskell layer (thanks to chrisbarrett)
• All base16 themes are now supported. For instance to add the tomorrow base16 variant: add base16-tomorrow to your dotspacemacs-default-theme variable.
• New banners directory. By default Spacemacs will randomly choose a banner to display. The behavior of banner display can be tweaked with the variable dotspacemacs-startup-banner, more info in the dosctring for this variable. You can now contribute banners!
• Use Magit built-in auto-completion based on ido instead of helm (thanks to bonega)
• New key bindings SPC f r for recently opened file selection (thanks to danielwuz)
• Better install instruction for the haskell layer (thanks to endrebak)
• Fix missing parenthesis on code snippets in documentation (thanks to bebound)