jira-integration: Increase size of field jiraLabels

As this field could be used to store a list of labels, it's better that it's
longer than 255 chars.

FEA: ItEr77S16JiraAndTimConnectorContributionIntegration
jira-integration: Allow to search labels by any chars and not only the first ones

Add simple comment explaining the purpose of SimpleListModelExt.

FEA: ItEr77S16JiraAndTimConnectorContributionIntegration