Little fixes and improvements

- Fix "let-alist" not found package, adding GNU "elpa" in source package
  lists;
- Ctrl+j and Ctrl+k scrolls down/up;
- Replace "goes-to-symbol" by "helm-semantic-or-imenu";
- ",q" now deletes window, instead of killing;
- ",f" replaced by ",a" to avoid annoying "evil-find-char";
- Adds evil-jumper plugin;
- Adds evil-visualstar plugin.