Improve unit testing docs in guide

[Narretz]

I think the unit testing part of the guide can be improved in major ways. From a quick glance:

1. It mostly talks about why unit testing is important, and how DI, separating logic from DOM etc. make code testable. This should be separated from the actual examples.
2. There's almost no reference to the default angular way of testing, i.e. there's no mention of angular-mocks, no mention of Karma (other than for the preprocessor). Jasmine is introduced in the middle of a paragraph
3. Other minor things:

• Examples use old controller syntax (controller on the window)
• Not mentioned how angular makes async tests sync (I got there from test($http): ignore date-toJSON test if running in IE8 #8219)

[RichardLitt]

I think we talked about the controller syntax in #5076. We agreed to change that for 2.0.

The other stuff certainly needs to be done.

[Narretz]

@RichardLitt with 'old controller syntax', I mean that very recently support for controllers on the window was removed, now they all must be defined in a module. I totally forgot about controller as as the new way.

[RichardLitt]

Ah, cool. Got a link for me to the window ref? I've missed that.

[Narretz]

Here, that's what I mean: 3f2232b My explanation maybe wasn't the best