Add regex support for OnAccessExcludePath

[b1tg]

Fix https://github.com/Cisco-Talos/clamav/issues/1074

To efficiently iterate over all watching files, I've introduced a linked list within struct onas_ht to keep track of all active buckets. Would this approach be effective for our purposes? @micahsnyder

[micahsnyder]

Rebased and squashed