Handling missing data, session caching

Changes

• Fixed caching problems (fixes #230, #228, #226, #225, #223, #187, #181; thanks @tomasz-soltysik!)
• Introduced session caching (closes #207, #198, #191, #186)
• Replaced API calls with async ones (fixes #196)
• Added reauth flow (fixes #208)
• Removed deprecated code (fixes #221)