BDD big BrowserContext refactor

Stuff to do:
- [x] Move ```BrowserContext.php``` into a separated folder
- [x] Clean ```BrowserContext``` (remove duplicated and deprecated functions)
- [x] Make Authentication sentences interface
- [x] Move all ```BrowserContext``` sentences definitions into a ```BrowserSentencesInterface```
- [x] Clean/refactor sentences definitions for browser interaction

If we follow this approach we can:
- have all sentences for interaction with an interface all together (in this case ```BrowserSentencesInterface```)
- have the 'generic' actions using only the interface interaction sentences  (ex: ```Authentication``` interface + ```AuthenticationContext```)
(sentences or content managing, but this will be presented on a later PR)
- With the sentences interfaces it will be easier to control a new feature/scenario to be implemented on all interfaces (ie: browser, rest, api)

The Feature folder will look like:
```
BehatBundle/Features
├── Context
│   ├── Browser
│   │   ├── BrowserContext.php
│   │   ├── BrowserInternalSentences.php
│   │   └── SubContexts
│   │       ├── BrowserSubContext.php
│   │       ├── AuthenticationContext.php
│   │       ├── ContentTypeGroupContext.php
│   │       └── ... all other sub contexts needed
│   ├── FeatureContext.php
│   └── SentencesInterfaces
│       ├── Authentication.php
│       ├── ContentTypeGroup.php
│       └── ... all other sentence definition interfaces
├── ContentTypeGroup                    - Feature group
│   ├── create_contenttypegroup.feature - Feature
│   ├── update_contenttypegroup.feature
│   └── ... other features
└── ... other feature folder&files

SomeOtherInterfaceBundle/Features
└── Context
    ├── FeatureContext.php                       - All needed (spefic) actions to interact with the interface
    ├── SomeOtherInterfaceInternalSentences.php  - The definition of the specific sentences for FeatureContext
    └── SubContexts                              - All implementations of the BehatBundle\SentencesInterfaces\*
        ├── SomeOtherSubContext.php
        ├── AuthenticationContext.php
        ├── ContentTypeGroupContext.php
        └── ... all other sub contexts needed

```

I'm currently using this for the REST BDD and it looks much more cleaner, since (here : https://github.com/MLoureiro/ezpublish-kernel/compare/bdd_rest_contenttypegroup ).
- have only the needed functions for the interface interaction here https://github.com/ezsystems/ezpublish-kernel/pull/797 
- the feature files are defined *only * at BehatBundle (with the respective sentences definitions on the interfaces)
- have the subcontext files with the sentences implementation (at the moment I'm only covering the create ContentTypeGroup and got 3 subcontexts ```Authentication```, ```ContentTypeGroup``` and ```ErrorContext```)