Graylog compat >= 2.0

• lowered Graylog compat to 2.0
• removed NumberFormat code for field values, not necessary and can cause problems with "wrong" Locales

Graylog 2.4 compat

• Changed required Graylog Server version down to 2.4.0, no need for 3.0.0-alpha :)
• some cleanup

Initial release

First working version