Two different modes: pedantic(slow)/lax(fast)

[mfalesni]

I was thinking about this before, widgetastic is currently very pedantic with page checking so it is relatively slow. There is a possibility to keep these check obligatory only after events like clicking and the rest would be invoked only if the selenium step triggers an error - like element lookup or such - and after the check the step would be repeated once more. The modes would be switchable.

This should only probably concern changes inside Browser class.