Add --game-list option to specify a file with filter regexes

[kblaschke]

The --game option will override the list as it's a more specific filter. This allows to configure the list globally in the config file while still using --game to download a single game via the command line.

With this change, the regexes are also only compiled once before filtering.

I went with a similar logic as it is applied with the --game option for the list file:

• If the file is found and contains at least one entry, games are filtered using the list
• If the file is found, but empty, no filter is applied (same as setting --game to an empty string)
• If the file if specified, but not found, no filter is applied either, but an error is printed.

To download all games without a filter while having a filter file specified in the config, users can simply reset it to an empty filename, e.g. lgogdownloader --game-list "".

Fixes issue #267