Improve dection of local/network video paths.

[tonycpsu]

• Replace simple "://" string check with a more thorough algorithm that considers the protocol string (if present) and any user-specified pathname patterns to be considered network paths.

• The following new settings govern this behavior:

  • thumbnail_network_protocols - pipe-delimited list of Lua patterns for network protocols

  • thumbnail_file_protocols - pipe-delimited list of Lua patterns for file protocols

  • thumbnail_network_paths - pipe-delimited list of Lua patterns that, when matched (and when network protocol checks don't match) determine that a file is on a network (e.g. /mnt/nas)