Better startup experience, "J" works like in Vim, fixes

Better startup experience

• This release optimizes the startup of spacemacs regarding the UI elements configuration and the display of the default theme (solarized-light). The startup should feel smoother with no flickering or flashing effect.
• This improvements may reduce the overall boot time of spacemacs.

Fixes

• J normal state command behaves like Vim J (thanks to bonega and danielwuz)
• Fix <SPC> f e d to open the spacemacs dotfile (thanks to capdevc)
• org-agenda-files can be defined in spacemacs dotfile (thanks to herbertjones)