Added group property to metadata field info.

A generic search application can use the group property to group related
fields together in the interface.
Simplified how property sensitivity settings work in the code.

Before, we would explicitly deal with the various "alternatives" such as
case/diac-sensitive, case/diac-insensitive, case-but-not-diac-sensitive,
etc. Now we simply use SensitivitySetting throughout (was already used
in indexing) with values ONLY_SENSITIVE, ONLY_INSENSITIVE,
SENSITIVE_AND_INSENSITIVE or CASE_AND_DIACRITICS_SEPARATE, covering most
needs. Additional SensitivitySettings could be added if needed.

In the unlikely case that you actually used the ability to manually add
additional alternatives, you should use additional properties for this
instead.
Added handling of case-sensitive-only or diacritics-sensitive-only.

Analyzers have been updated to not only handle the fully sensitive /
fully insensitive cases, but also the separate cases for case- and
diacritics sensitivity.
Made it possible to query the BlackLab build time.

To find out when the currently running BlackLab JAR was built, call
Searcher.getBlackLabBuildTime(). To find the build time of the BlackLab
JAR used for indexing, call IndexStructure.getIndexBlackLabBuildTime().