Make the list of modules loaded by Prelude configurable.

Modules loaded by Prelude can now easily be adjusted via
the file `prelude-modules.el` in Prelude's installation folder.
To disable a module simply comment it out; conversely uncomment
a module to enable it.
Auto-install slim-mode.
Map Command to Meta as well.
Remove dubious workaround for package.el timeout problem.
Fix #255.

`prelude-duplicate-current-line-or-region` was broken after the introduction of
dash.el.
Fix #261 - add missing dot in directory name
Display truly "random" tip on startup
Open ansi-term buffer in another window
Introduce prelude-visit-ielm command and bind it to C-c C-z (a-la-slime)
Merge branch 'master' of github.com:bbatsov/prelude
Adding personal files..
adding personal files
merging with batsov
Merge remote-tracking branch 'batsov-branch/master' into work-branch
remove annoying greeting