[common] Add IssueSummary class

This class stores the summary of an issue, so far, the id of
the issue and the last time it changed.
[Bugzilla] Remove deprecated BugzillaIssueSummary class

This class was deprecated since IssueSummary is in
'common' module. Now, the parser uses the common class.

Unit tests updated.
[Redmine] Add RedmineIssuesSummary class
[tests] Check empty list initializing RedmineIssuesSummary
[Redmine] Add Redmine issues summary parser