WebRunner FindSteps should allow auto-completion of step patterns

As noted on the users' list, it'd useful for the WebRunner to allow auto-completion of step pattern in the FindSteps page.

Add an 'Explore' section where a user can start typing any part of a step pattern and get shown a list of patterns that are annotated in the candidate steps classes.

Once a pattern has been chosen, the method (and class) can also be shown.

Note that exploring the step pattern is different from matching the textual step. A given textual step can be matched by multiple step pattern.