Pattern Checker support for target-only case

[YvesS]

There are cases when an issue is best defined when the target matches a given pattern. Without comparing things with the source.

For example:

• The user may want to trigger an issue when some type of punctuation is found in the target.

• Or the user may want to detect apostrophe used between words in the target (like in French or Italian) and ensure they are the "curly" type rather than the ASCII type.

• Or the user may want to detect types of quotes that are not appropriate for a given target language.

[YvesS]

Implemented in https://bitbucket.org/okapiframework/okapi/commits/30d69415cc0a34b39a6d966643083907ff9072be