[FEATURE]Home page- add 'Subscribe to Newsletters' button

[akrajna]

Describe the solution you'd considered

Add 'Subscribe to Newsletters' button to the home page under the banner as below:

After pressing the button 'Subscribe to Newsletters' an input field appears where has to write his email address. After filling in the email input field and pressing 'subscribe' user is subscribed and will receive newsletters tho given email.

Acceptance criteria

• the 'Subscribe' button is added to the home page under the banner
• after pressing the button 'Subscribe to Newsletters' an input field appears where user can write his address
• the email input field appears above the 'Subscribe' button
• after filling in the email field and pressing 'Subscribe' button again user is subscribed and will receive newsletter messages on the mail address he added
• if user leaves the email field empty and presses the 'Subscribe' button again the information in red color 'Please enter a valid email address' appears under the input field