Mark entities with content pack they've been created from

Added attribute to Input, Output, Dashboard, Stream, and StreamRule which marks
from which content pack (by name) it was created from.

Refs Graylog2/graylog2-web-interface#937
Reduce number of empty/anonymous collections flying around
Ensure that searchHits is not null in AlertConditions

Under some conditions FieldValueAlertCondition#getSearchHits and MessageCountAlertCondition#getSearchHits
could return null which caused problems further downstream, when consumers of the respective AlertCondition
expected to always get a list of messages (though being empty if there weren't any search hits).

Refs Graylog2/graylog2-alarmcallback-slack#1
Add support for content pack marker in REST client

Refs Graylog2/graylog2-web-interface#937
Use content pack ID instead of name (which might be ambiguous)

Refs Graylog2/graylog2-web-interface#937
Add a Syslog octet counting frame decoder. (RFC6587)

See: http://tools.ietf.org/html/rfc6587#section-3.4.1
Add SyslogTCPOctetCountInput and SyslogTcpOctetCountTransport.
Handle both TCP syslog framing methods in a SyslogTcpTransport.

Also adjust to refactored transports.
Rename framer handler to avoid name clash.
Add missing license.
Remove duplicate license.
Do not use isDigit() and check if buffer is readable.
Test that the buffer does not get mutated.