Add bootstrap dependency

Bootstrap used to be installed by other components, but is no longer, this caused the example code to not work as advertised.

Note:
There is still a bug in angular-strap that makes some of the selects not work properly.
However, that is easy to work around by initializing the arrays.
It will likely be fixed in the next angular-strap release.

Note # 2: The workaround has after this release been applied to most of the selects in the example, as it is also a test bed.