Refactor API code

[abitmore]

• Avoid wrapping heavy database_api objects in other API classes
  • Move some code from database_api_impl to a new class database_api_helper, and let database_api_impl inherit from database_api_helper
• Avoid magic numbers in code / doc about API limits
  • Add api_limit_get_market_history to app_options
  • Add api_limit_get_full_accounts_subscribe to app_options
• get_margin_positions API now is implemented with get_call_orders_by_account, and only returns the first page
• Simplify implementation of some APIs by using template functions
• Fix code smells

[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
13 Code Smells

71.2% Coverage
0.3% Duplication