[DBClientConfig] Add a structure to store connection information of an issue tracking system
[DBClientConfig] Inherit MonitoringServerInfo to define ITSInfo

Because now I'm planning to implement syncing issues as Hatohol's
Arm.
[DBClientConfig] Revert 3ca2bf6b

Abort inheriting MonitoringServerInfo on defining ITSInfo to build
prototype ASAP.
[DBClientConfig] Add a definition of issue_trackers table
[DBClientConfig] Initialize issue_trackers table on starting hatohol
[DBClientConfig] Add "id" and "type" columns to issue_trackers table
[DBClientConfig] Rename a structure

ITSInfo ->
IssueTrackerInfo
[DBClientConfig] Fix wrong table names in COLUMN_DEF_ISSUE_TRACKERS
[DBClientConfig] Add "nickname" column to issue_trackers table
[DBClientConfig] Add a function to add an issue tracker
[testDBClientConfig] Test validation of addIssueTrackerInfo()
[testDBClientConfig] Remove needless code
[DBClientConfig] Use vector instead of list to pass multiple IssueTrackerInfo

github issue #178
[DBClientConfig] Fix a typo
[DBClientConfig] Add a function to get IssueTrackerInfo
[testDBClientConfig] Fix wrong expected data for getting IssueTrackerInfo by INVALID_USER_ID

The test should fail because it's not implemented yet.
[DBClientConfig] Add a new class IssueTrackerQueryOption
[testDBClientHatohol] Add tests for IssueTrackerQueryOption
Add a skeleton of a new class "IssueSenderRedmine"

This class will manage sending issues to Redmine via REST API.
[ZabbixAPIEmulator] Extract fundamental http server related code as a super class "HttpServerStub"

I'll add RedmineEmulator to test IssueSenderRedmine