Adds select2-fallback to web_steps.rb

`When I select [...]` previously only selected from actual inputs of
type select. When that selection fails due to select2 only loading the
possible options on demand, i.e. when opening the select, web_steps will
try to activate said select2 instance. This approach allows for writing
of cukes w/o worrying what select implementation is used and has litte
impact on traditional selects.
Merge pull request #4 from finnlabs/feature/select2-select

Adds select2-fallback to web_steps.rb