refactor(datepickerSpec): speed up tests

Tests were compiling the element multiple times unnecessarily as it's
done in the root describe's beforeEach.

Introduce describe blocks with no name to encapsulate tests that need
the element to be compiled and separate them from tests that have their
own compilation.

Using the `reportSlowerThan` option of karma, I found that the datepicker tests are running the slowest. This is also an indication that we might have a lot of watchers in datepicker. It's a rather complicated widget.

No changes in the testing at all. Only indentation and moving things around.

Before:
![screen shot 2013-12-30 at 8 18 31 pm](https://f.cloud.github.com/assets/132584/1825757/aa29716e-71d2-11e3-94e2-7138f3967273.png)

After:
![screen shot 2013-12-30 at 8 18 05 pm](https://f.cloud.github.com/assets/132584/1825758/ae58433c-71d2-11e3-98e1-ce61d16a9c14.png)