Mechanism to count errors within Tigase

A new processor within statistics has been added to count the number of errors that Tigase returns. This processor, named error-counter, will count all errors returned by Tigase, however by default the number is always zero if it is not enabled. It can be found as an MBean object in JMX under ErrorStatistics and contains values for packets with ERROR and grouped by type. To enable counting of these errors, you must ensure the processor is included in your sess-man configuration:

'sess-man' {
    'error-counter' () {}