Codeception functional tests

3 functional tests with Codeception. Executed with `php codecept.phar run`.
Discussion creation, Post Reply is tested.

The test can be reviewed in `tests/functional`.
Result:

```
Functional Tests (3) ---------------------------------------------------------
Trying to reply in a discussion (ReplyInDiscussionCept.php)              
Scenario:
* I have record "Phosphorum\Models\Users",{"name":"Phalcon"}
* I have in session "identity","237"
* I have in session "identity-name","Phalcon"
* I have record "Phosphorum\Models\Categories",{"name":"Testing","slug":"test"}
* I have record "Phosphorum\Models\Posts",{"title":"Please help with testing","content":"How can I install Codeception","users_id":"237","slug":"please-help-with-testing","categories_id":"132"}
* I am on page "/discussions"
* I see link "Please help with testing"
* I click "Please help with testing"
* I see "Please help with testing","h1"
* I fill field "#content","I can do that!"
* I click "Add Comment"
* I see "I can do that!",".post-content"
 PASSED 

Trying to perform shadow login as first user (ShadowLoginCept.php)       
Scenario:
* I have in session "identity",1
* I have in session "identity-name","Phalcon"
* I am on page "/"
* I see "Logout"
 PASSED 

Trying to start a discussion (StartDiscussionCept.php)                   
Scenario:
* I have record "Phosphorum\Models\Users",{"name":"Phalcon"}
* I have in session "identity","238"
* I have in session "identity-name","Phalcon"
* I have record "Phosphorum\Models\Categories",{"name":"Testing","slug":"test"}
* I am on page "/"
* I see "Start a Discussion"
* I click "Discussions"
* I click "Start a Discussion"
* I see "Start a Discussion","h1"
* I see record "Phosphorum\Models\Categories",{"name":"Testing"}
* I fill field "#title","How can I write tests in Codeception"
* I fill field "#content","Is there any manual"
* I select option "#categoryId","Testing"
* I click "Submit Discussion"
* I see "How can I write tests in Codeception","h1"
* I see in current url "/how-can-i-write-tests-in-codeception"
 PASSED 
```