Added CSRF protection in Email account setting page
Removed SupportFlow_Email_Accounts::get_email_accounts method allowing direct data access
Splitted SupportFlow_Email_Accounts::settings_page in multiple smaller methods
Made minor changes to E-Mail accounts settings page

Renamed is_exist_email_account method with email_account_exists
Corrected I18n format using sprintf
Used esc_attr instead of esc_html for escaping attributes
Fixed implementation of sanitize_text_string