Change a structure for setup and connection inforation of DB.

I decided to clean up the code drastically, because
there are the following tree motivations.

(1) To remove a complicated setup mechanism
Previously, DB setup and connection information is stored in
the class: DBClientConnectable that is a template class and
has static members. In addtion, it manages connectionInfo
doubly. They are results of extension that was done every
time it were needed.

(2) Compatibility between compilers
clang compiler is incompatible with g++ in terms of the handle
of static member in a template class. They cause different result.
So we remove the template class itself that is one of the things
that make code complicated.

(3) To be the base class of DBClientZabbix
The previous structure doen't handle a DBClient derived classes
that uses a dynamically generated DB domain ID.
Replace the header file name.

DBClinetConnectable:
The previous base class that is a template class.

DBClinetConnectableBase:
The new base class that stores setup and connection information
in the map, instead of making some template bodies corresponding
to the DB domain ID.

This class name is a little long. I will change it latter or
merge it into DBClient.
Set a DB server of DBClientAction.
Removed unused variables.
Implement DBClientConnectableBase::reset().
Call parseCommandLineArgument() surely.
Remove an unused variable.
Reset ConnectionInfo instances on DBClientConnectableBase::reset().
Use two-phase lookup in order not to degrade the performance.
Use DBClientConnectableBase to make code simple.
Merge DBClientConnectableBase into DBClient to be simple.
Remove DBClient::setDBAgent(), because it is not necessary.
Make parseCommandLineArgument protected to promote encapsulation.
Remove an unused parameter.
Add a file for quick reference.
Fix the problem that doesn't wrap.
Set the default database name for config.
Add a check for the return value of parseCommandLineArgument().
Add the default user and password for config.
Clean up with the previously added helper function.