Target regexp and priority cleanup

* Make sure periods are always escaped
* Where appropriate, always start with "^https?://"
* For optional subdomains, always use "([^/]*\\.)?", for mandatory subdomains, use "[^/]+\\."
* Remove all instances of non-capturing parentheses and replace with capturing parentheses. This doesn't matter in target regexp and makes it a bit cleaner.
* Adjust priorities based on #765 (probably not exhaustive)

Possibly unnecessary and I'm not sure how great such a huge amount of translator updates is on Zotero servers. I'm going to do a general cleanup of `processDocuments`, `doGet`, `doPost` calls to use relative or at least protocol-relative URLs because of breakage in Chrome, so this should probably wait until the next commit.