Improved proxy setup

[Lezek123]

Improves proxy setup by introducing:

• faulty proxy exclusion (in case a proxy endpoint is blocked, it's temporarily excluded from use)
• proxy binding per video (all requests related to the same video use the same proxy)
• waiting period if no proxies are available (the app will wait if all of the proxy endpoints are either already in use or are excluded/disabled)
• configurable "intermediary" proxychains endpoint (if required in order to access proxies listed in config.proxy.urls)
• proxy for thumbnail downloads (addresses: Downloading thumbnail does not use socks proxy #340)
• improved logging to easier identify faulty proxies