[server][ArmStatus] Add a new stub class: ArmStatus.
[CodingConvention] Add a rule.
[CodingConvention] Improve the sentence for readability.
[CodingConvention] Use the same header name for readability.
[mlpl][SmartTime] Add a new operator '=='.
[mlpl][testSmartTime] Add a new test: test_operatorEqualDiffNSec().
[mlpl][testSmartTime] Add a new test: test_operatorEqualDiffSec().
[server][mlpl] Add a new operator: <<(ostream, SmartTime).
[server][mlpl] Add a missing 'const'.
[server][mlpl][testSmartTime] Clean up.
[server][mlpl][SmartTime] Add a new cast operator.
[server][mlpl][SmartTime] Reimplement ostream &operator<<() with the cast operator to string.
[server][ArmStatus] Add a new method: getArmInfo().
[server][ArmZabbixAPI] Use a defined type to increase flexibility.
[server][DataStore] Add a new virtual method: getArmBase().
[sever][DataStore] Replace a return type from a pointer to a reference.
[server][DataStore] Remove collectArms().

The function collects ArmBase instances from a DataStore.
However, current code supposes one DataStore has one ArmBase.
So getArmBase(), added in the recent commit, can be replaced with
it.
[server][UnifiedDataStore] Fix a style.
[server][UnifiedDataStore] Clean up.
[server][UnifiedDataStore] Narrow a range of a variable.