Refresh to Travis CI configuration.

This commit updates the Travis Continuous Integration configuration to
make it work again.

I chose a different approach to installing the SDK, that avoid depending
on the order in which things are returned by the tool and breaks each
time something changes (like a new release). Instead use static links to
the SDK components that we need.

Since the continuous build is not reliable enough (or at least I am not
sure it is), also only notify myself of failures.
Merge pull request #33 from hssm/default-font-selector

Use less specific CSS selectors for the default font.
Correctly handle calls to constructors.

Make sure we always call the super constructor because they might set a
default style and this would be lost if we call it with zero.
Merge pull request #31 from flerda/v2.1-travis

Refresh to Travis CI configuration.
Merge pull request #35 from flerda/v2.1-preference-constructors

Correctly handle calls to constructors.
Preferences and strings for collection preferences