Provide NLS support in JGit.

The support for NLS relies on java.util API to load a standard
ResourceBundle and then uses java reflection API to inject localized
strings into public String fields of the corresponding instance
of TranslationBundle.

Locale setting is supported per thread to enable concurrent threads
to use different locales. This is useful when JGit runs in a server
context where (error) messages might need to differ per-request to
suit the user's preference.

Change-Id: Ie0e63a0d7bb74eaad495dbe8248595d8a3a76883
Signed-off-by: Sasa Zivkov <sasa.zivkov@sap.com>