Code refactor and new client side individualization impl

[MrDini123]

Hi,

This PR wants to target the new client side individualization technique HBO uses for a week (or so) however I decided to refactor the code first. It's going to be a rather huge PR.

Planned things:

• Fresh code style (better readability)
• camelCase to underscore variables
• instead of referencing dict keys directly, use dict.get() calls when necessary (partly done)
• replace string concat with format strings
• instead of global variables, maybe use hidden settings entries (feedback needed)
• more flexible if syntax everywhere
• rely on requests and drop urllib2 everywhere to make HTTP calls
• new client side individualization

As always, any feedback is welcome

[MrDini123]

Okay, that's it for now. I have decided not to take care of the uncomplete checkboxes yet in this PR since the whole listing would require a complete redesign. I plan to address those in a future PR. However after testing most things out everything seems to be working fine (tested under Windows x64; Kodi 18.3 & Kodi 18.2 LE; Raspberry Pi2 - however if you can, please try it on other devices).

Should be done for prod and up to you to merge or ask me to change if required.

PS: If this is going to be merged, please go for the squash merge method if possible. So all the commits will be converted into one large.

Thanks for this awesome addon!