Overall improvements to API access

[Jopyth]

Fixes #19.

Changes (finished and unfinished):

• [x] Reload contacts in specified interval
• [x] Filter calls connected to real devices (to distinguish between connected calls and voice mail)
• [x] Add small minimal padding margin between caller and time
• [x] Add error codes (if showContactsStatus is enabled)
• [x] Removed some debug prints (can be shown with debug: true in config)
• [x] Update README.md
• [ ] See if #20 can be debugged better with this (or is it maybe even fixed?)
• [ ] Someone else also should test the whole thing and verify it works (+ find possible unclear config options)