Add a Browser layer for BDD tests

Adding a Browser layer between FeatureContext of BehatBundle and DemoBundle will make possible to:
- have all code generic for any API (PAPI, REST, or Browser Interfaces)
- all generic browser actions on BrowserContext

Behat has a known limitation that is the RegEx must be unique, can only exist once, so if we got a sentence like:
- "Then I see search 1 result" 

so for a browser interface such as DemoBundle the code for asserting total search results is different form PAPI or REST. and this being implemented on BehatBundle FeatureContext would make impossible to redefine this for the others API's.
Also defining this on DemoBundle FeatureContext wouldn't be a pleasant option, since to test other browser interfaces the code needed to be copy pasted to all other interfaces duplicating the code and with it bringing all the code maintenance problems.

There will be a PR's also for DemoBundle changing the inheritance of the FeatureContext, I'll post here the link as soon as it is done.

Edit: 
DemoBundle PR: https://github.com/ezsystems/DemoBundle/pull/26