INTEXT-118: Fox for long messages with newlines

JIRA: https://jira.spring.io/browse/INTEXT-118

It also tests long messages without newlines to verify that the fix works for both types of long messages.

INTEXT-118: Replace regular expression split with standard substring to split message into subparts with max length.
The regular expression used earlier failed splitting messages that contained newlines correctly. (See SmesMessageSpecificationTest)

Corrected spelling in constants

Polishing