iedit, colors, whitespaces, aggressive-indent, tweaks and fixes

• Move iedit layer to spacemacs layer, see documentation
• New contrib layer colors
• New toggle SPC t SPC to toggle visibility of whitespaces (thanks to Khaki)
• Add aggressive-indent-mode, disabled by default, can be toggled with SPC t i
• Fix fancify symbols initialization in clojure layer (thanks to vijaykiran)
• Fix and enable helm-semantic-or-imenu on SPC s l for javascript layer (thanks to danielwuz)
• Remove use-package sub-module. It is now a bootstrap package. Spacemacs will now correctly get the latest version of use-package available in MELPA.
• Fix n and N bindings in all evilified buffers.
• Fix git-guttter lazy loading and initialization
• Fix perforce layer which was completely broken