Helm cleanup

The code of prelude-helm module, with ugly formatted code and many typo and grammar mistakes, is really a mess. I know helm is a gigantic package, but it does not require that much code to configure. Many options are not necessary and most of the keys are subjected to personal taste. I think most of the code in the helm module is too personal to make it part of prelude, we should leave most of the customisable options to the users, and have a bare minimal working configuration like this one:

https://gist.github.com/toctan/ac523ef379f14f5486e2 

In this pull request, I removed all the options which are already the default and thus are not necessary and fixed some typos.
@toctan As far as I know, we don't have a reliable way to detect such window layout. Think if you have 3 windows, two smaller windows on the left and one big on the right and point is in one of smaller window, how do you know which is vertical, which is horizontal since both are available?

It seems you use a laptop screen and your laptop is small. You have a few options to workaround this problem:

- Don't use `helm-split-window-in-side-p`. Use `helm-split-window-default-side ` and set it to `'other`. When you only have one window, it opens Helm buffer below, but when you have two or more windows, it opens Helm buffer in other window, preventing Helm buffer to override your current working buffer.

- Use `helm-always-two-windows` that always open two windows: your current selecting window and your Helm buffer when you use a Helm command. Original window layout is restored when you quit the Helm session.

Actually now I think it again you could just `remove helm-split-window-in-side-p`. I think it's better to use `helm-split-window-default-side ` and set it to `'other` since it's more inline with Helm's default `below`.