Vim: Replace vim-snipmate with a new bundle 'ultisnips'

Ultisnips is better than vim-snipmate, and also has great
compatibility with the previously existing vim snippets.

Shortcuts mapped to <Ctrl-j> and <Ctrl-k>.
Vim: Polishing settings

- Polish folder comments
- Disable remebering last position for some filetypes
- Key mapping for <leader>f (CtrlPF)
- Fix guifg for SpecialKey highlight