User params

### Details ###
This will introduce user params functionality. Currently only two parameters are supported:
- language
- timezone

Notice that a new global template variable is introduced - `offset`. This will allow to modify dates accordingly. A global `lang` template variable now contains user's language param.

Please note that params are applied only after re-login.

### How to test ###

1. Pull the `user-params` branch
2. Switch the language using language switcher when you are not logged in. The language should switch accordingly.
3. Login and switch the language using language switcher. The language should switch accordingly.
4. Under the user menu choose "Profile". The "Edit user" page should open showing two params: "Language" and "Timezone". These should be as default ones: Language - "en-GB", Timezone - "UTC"
5. Click the "Cancel" button. You should be redirected to the "My profile" page.
6. Under the user menu choose "Profile". Change the language and timezone and click "Save". Selected language should be saved, but the display language should stay the same as you selected in item 3.
7. Logout and login. The language should change to the value that you saved in item 6.
8. Switch the language using language switcher. The language should switch accordingly.
9. Under the user menu choose "Profile". Ensure that the language and timezone values are the same as you saved them in item 6.
10. Test is passed :+1: 

### Current issues ###

Twig does not apply the timezone. For now I can't find why. For example this does not work:
`activity.created_date|date("j M y", offset)`

But this works:
`"now"|date("j M y", offset)`