Fix Date::fromDbStringLocal() when YYYY-MM-DD is given (modify issue #75)

[FujiwaraNaoto]

abstract

I fixed Date::fromDbStringLocal() bug ,which is mentioned here

Cause of the bug

in Date::fromDbStringLocal(const std::string &datetime)
function std::vector<std::string> &&v = splitString(datetime, " "); is used.

when argument datetime format is YYYY-MM-DD, then v.size() equals 1 and program doesn't pass through if (v.size() == 2).

implementation

1. add unit test when format YYYY-MM-DD is given.
2. modify Date::fromDbStringLocal() function to adapt format YYYY-MM-DD. in this case, v.size() is 1

[FujiwaraNaoto]

Could you review this pull request?